Daniel's been looking at the global roaming landscape and he's got a question that starts practical but digs into something deeper. He travels a lot, he's already using SIP for voice and eSIMs for data profiles, and he's noticed that the space is absolutely stuffed with marketing — worldwide data plans, unlimited global roaming, all of it. So he wants to know: what's actually legitimate? Is there a SIM card, or an eSIM, that can reliably provide data in most countries for an affordable monthly fee? And is that even a realistic thing to ask for?
Right.
But then he pulls back a layer. He wants to understand how the economics of data roaming actually work under the hood. When you land in a country and your phone lights up on the local network, what just happened? How did that foreign carrier decide to let you on? What governs the authentication, the billing, the whole handshake? He's asking us to explain the plumbing and then tell him what's worth buying.
So we've got two things to do here. One is the engineering answer — the signaling, the wholesale agreements, the way a phone from one country authenticates on a network in another. The other is the market answer — what's actually available, what's a fair price, and whether the global roaming promise is real or mostly marketing.
Let's start with the plumbing. I want to know what happens in the first three seconds after the plane lands and I turn off airplane mode.
Okay. The thing to understand is that international roaming is not some modern add-on. It's built into the GSM standard from the beginning. The whole architecture was designed for this. When your phone powers on in a foreign country, it scans for available networks and picks one — either automatically based on preferences stored on the SIM, or manually if you've set it that way. The foreign network sees your phone's IMSI, the International Mobile Subscriber Identity. That's the fifteen-digit number on your SIM card that uniquely identifies you.
So the foreign network sees a number it doesn't recognize and says... what?
It doesn't say no. It says, I don't know who this is, let me ask around. The foreign network is called the VPMN — Visited Public Mobile Network. Your home carrier is the HPMN, the Home Public Mobile Network. The VPMN sees your IMSI and the first few digits tell it what country and what carrier you belong to. Those first five or six digits are the MCC and MNC — Mobile Country Code and Mobile Network Code. So the VPMN knows immediately, this is a phone from, say, an Israeli carrier, or a US carrier, or whatever.
And then it sends a message home.
It sends a signaling message over SS7 — Signaling System Number Seven, which is the backbone protocol for carrier-to-carrier communication — to your home network's HLR, the Home Location Register. The HLR is the database that knows where you are and what services you're authorized to use. The VPMN says, I've got this subscriber, IMSI such-and-such, requesting to attach. The HLR checks your account. Are you allowed to roam? Is your bill paid? What services are provisioned? And if everything checks out, the HLR sends back a set of parameters that authorize the VPMN to create a temporary record for you in its own VLR, the Visitor Location Register.
So the foreign network creates a temporary local profile for me.
Right. And your home HLR updates its own record to say, this subscriber is now on this foreign network. From that point, calls and data to your number get routed internationally. The whole thing happens in a few hundred milliseconds. The technical term for the authentication handshake is the MAP — Mobile Application Part — protocol. It's a set of SS7 messages: sendAuthenticationInfo, updateLocation, insertSubscriberData. These are the actual commands flying between carriers.
That's the authentication piece. What about the billing? How does the foreign carrier get paid for letting me use its towers?
This is where the economics get interesting. Carriers don't negotiate individual roaming deals for every subscriber. They sign wholesale roaming agreements with each other. The GSMA — that's the industry trade body — maintains a standard template for these agreements. It's called the GSMA Roaming Wholesale Agreement, and it covers things like the inter-operator tariff, which is the per-megabyte or per-minute rate that the visited carrier charges the home carrier. So when you use data in France on a US SIM, the French carrier bills your US carrier at the wholesale rate. Your US carrier then marks that up and bills you at the retail rate.
So there's a spread. The home carrier is buying data wholesale and selling it to me retail.
And that spread can be enormous. Wholesale roaming data rates have come down dramatically over the past decade — the GSMA has pushed for lower inter-operator tariffs, and the European Union regulated retail roaming surcharges out of existence within the EU. But outside regulated zones, the wholesale rate might be somewhere between one and five dollars per gigabyte, depending on the carriers and the countries involved. The retail rate to the consumer can be ten, fifteen, even twenty dollars per gigabyte. Some carriers still charge by the megabyte.
So when I see a plan that offers global roaming included, what's actually happening is that the carrier has negotiated a large enough basket of wholesale agreements that they can absorb the cost into the monthly fee, and they're betting most subscribers won't use enough data to blow past the margin.
And this is the core of why Daniel's question is tricky. A truly global data plan that works everywhere at an affordable price is fighting against the basic economics of wholesale roaming. Every megabyte you use in a foreign country costs your carrier real money, paid to the visited network. There's no way around that unless the carrier owns infrastructure in that country, which almost none of them do outside their home market.
So what are the actual options? Daniel asked what's legitimate.
There are three categories worth looking at. The first is the traditional carrier global roaming plan. Think of the major US carriers — T-Mobile, AT&T, Verizon — they all offer international roaming add-ons. T-Mobile's had the most generous approach historically, with free data roaming in over two hundred countries, but it's throttled to two hundred and fifty-six kilobits per second on the base plan. That's enough for messaging and maps, not for streaming. The higher-speed passes cost extra. The second category is the travel eSIM providers — companies like Airalo, Holafly, Nomad, Ubigi. These are not carriers themselves. They're resellers.
Resellers of what?
They buy wholesale data from carriers in multiple countries and package it into regional or global eSIM plans. They're essentially arbitraging the wholesale market. Airalo, for example, has a global eSIM that covers over a hundred countries, but the pricing varies by region and data amount. Holafly goes for unlimited data plans but throttles after a certain threshold. The key thing about these providers is that they're typically data-only. You don't get a phone number. You're buying a data pipe, and you use SIP or VoIP apps for calling.
Which fits Daniel's setup. He's already doing SIP for voice.
Right. The third category is what I'd call the MVNO experimenters — companies like Google Fi, which was innovative on this front. Google Fi's whole pitch was that it had roaming agreements with carriers in over two hundred countries, and you paid the same ten dollars per gigabyte whether you were at home or abroad. They ate the wholesale cost difference. The catch was that this was never sustainable as a standalone business — it was subsidized by Google's broader strategy. And even they've tightened the terms over the years.
So the global roaming promise isn't a lie, but it's a loss leader or a throttled service almost everywhere you look.
The physics of the situation is that data costs money to move. A carrier in Thailand has to pay for spectrum, towers, backhaul, power. They're not going to let a foreign subscriber use that infrastructure for free. So someone has to pay the wholesale rate. Either you pay it directly through a per-gigabyte roaming charge, or you pay it indirectly through a higher monthly fee that covers the carrier's wholesale costs, or you accept throttled speeds that keep the usage low enough that the carrier's wholesale bill stays manageable.
What about the eSIM angle specifically? Daniel mentioned that eSIMs make it easy to have lots of profiles. Does that change the economics, or just the convenience?
Mostly the convenience. But convenience matters. With a physical SIM, switching carriers in a new country meant finding a shop, buying a plastic card, waiting for activation, and physically swapping the tray. With eSIM, you can buy a data plan from Airalo or Holafly while you're still in the air, scan a QR code, and have it active before you land. The cost of switching has dropped to near zero. That means the market for travel data is becoming more competitive, because you're not locked into whatever your home carrier charges for roaming. You can shop around.
So the eSIM doesn't fix the wholesale cost problem, but it makes the reseller market viable.
And that's what we're seeing. The travel eSIM providers are multiplying because the barrier to entry is low — you don't need to build a network, you just need to negotiate wholesale agreements and build an app. The fragmentation is wild. There are dozens of these companies now, and the quality varies enormously.
Let's get specific. If Daniel wanted a single eSIM that covers most countries with usable data at a predictable monthly cost, what's the closest thing to that?
I'd say there are three contenders worth naming. First, Google Fi's Flexible plan still exists, and for someone who travels constantly, the ten dollars per gigabyte rate capped at sixty dollars for data — after which it's free — is hard to beat. But it's only available to US residents, and they'll cut you off if you're abroad for more than about ninety consecutive days. They enforce that aggressively now.
So it's not a global solution for a global person.
Right. Second option is the Airalo Discover global eSIM. It covers over a hundred and twenty countries, and the pricing is straightforward — you buy a data package that's valid for a set period. A twenty-gigabyte package valid for three hundred and sixty-five days runs about eighty-nine dollars. That's about four dollars and forty-five cents per gigabyte. Not bad, but you have to manage your usage. Third option is Holafly's unlimited global eSIM. They offer unlimited data in over a hundred and sixty countries, but there's a fair-use throttle after a certain amount per day. The pricing is higher — around ninety-nine dollars for thirty days, or cheaper if you commit to longer periods.
So the unlimited one is a hundred bucks a month, roughly.
Give or take. And the "unlimited" is not truly unlimited. There's always a throttle. The fair-use policy kicks in somewhere between one and three gigabytes per day depending on the country. After that, you're down to half a megabit or less.
Which is still usable for email and maps.
It is. But it's not the same as having a real local data plan. And this is the thing I think most people don't realize about global roaming products. They're convenience products. You're paying a premium for the convenience of not having to think about it. If you're willing to spend five minutes buying a local eSIM in each country you visit, you'll almost always get better speeds and lower prices.
That's the trade-off. Convenience versus cost and performance.
And the convenience is real. If you're landing in three countries in a week, the overhead of researching and buying a local plan in each one is significant. But if you're spending a month in one place, the global roaming plan is probably the wrong tool.
Let's go back to the wholesale economics for a minute. You mentioned the GSMA template agreement. What's actually in those wholesale rates? How do they get set?
The inter-operator tariff is negotiated bilaterally between carriers. There's no central clearing price. A large carrier like Vodafone, which has operating companies in many countries, can negotiate better rates because it can offer reciprocal roaming to the other carrier's subscribers. A small MVNO or reseller has less leverage. The rates also vary by country. Roaming in a country with high spectrum costs and expensive infrastructure — Switzerland, Japan — costs more than roaming in a country with lower costs.
So the reseller's margin is squeezed between the wholesale rate they pay and the retail price they can charge.
Right. And the retail price is capped by competition. If Airalo charges too much, you'll just buy a local SIM instead. So the resellers are operating on thin margins and betting on volume. Some of them are probably losing money on customer acquisition right now, trying to build a user base.
Which means some of them won't be around in two years.
Almost certainly. The travel eSIM market is in its consolidation phase. We'll see a few winners and a lot of dead companies.
What about the authentication side of this? Daniel asked specifically about how the foreign carrier grants access to your subscriber ID. Is there a security angle here?
There is, and it's worth understanding. The authentication in GSM roaming uses a shared secret key stored on your SIM card and in your home carrier's authentication center, the AuC. When the VPMN requests authentication, the home AuC generates a random challenge and computes the expected response using the shared key. The VPMN forwards the challenge to your phone, your SIM computes the response, and the VPMN compares it to the expected response. If they match, you're authenticated.
So the foreign carrier never sees the actual key.
Never. They only see the challenge and the response. The key stays on your SIM and in your home AuC. This is actually a well-designed system from a security standpoint. The vulnerability is in the SS7 network itself. SS7 was designed in an era when the only entities on the network were trusted national carriers. It has no built-in authentication for signaling messages. If an attacker can get access to the SS7 network — which has happened through compromised carriers or signaling hubs — they can send fake signaling messages, intercept SMS-based two-factor authentication codes, track a subscriber's location, all sorts of things.
So the roaming handshake is secure between the phone and the home network, but the carrier-to-carrier signaling that makes it possible runs on a network that assumes everyone on it is a friend.
That's exactly the problem. And it's been known for years. The industry has been migrating to Diameter signaling for 4G and 5G networks, which has better security, but SS7 is still widely used for 2G and 3G fallback and for inter-carrier roaming in many regions.
That's... not great.
It's not. But for the consumer, the practical risk is low unless you're a high-value target. The bigger practical concern with roaming is the cost surprise. People land, turn on data, and get a thousand-dollar bill because their phone downloaded updates in the background.
Which is why Daniel's asking about predictable monthly pricing.
Right. And the honest answer is that truly predictable global data at a flat monthly rate doesn't really exist yet, unless you're willing to accept throttled speeds or you're paying a premium that effectively pre-pays your wholesale usage. The closest thing is probably a combination approach. Keep your home carrier's basic roaming for calls and SMS, and use a travel eSIM for data. Or go full SIP for voice and use data-only eSIMs everywhere.
That second approach is basically what Daniel's already doing. He's asking if there's a single eSIM that can replace the patchwork.
And the answer is... sort of. The Airalo Discover global plan is probably the closest to what he's describing. One eSIM, one hundred and twenty-plus countries, one price per gigabyte, a year-long validity. But it's not unlimited, and it's not cheap enough to be a no-brainer. He'd still need to track his usage.
What about the carriers that claim to offer truly global unlimited data? The ones with the glossy websites and the "worldwide coverage" maps?
Most of those are marketing operations built on top of the same wholesale reseller model. They buy capacity from the same wholesalers that Airalo and Holafly use, wrap it in a prettier package, and charge more. Some of them are outright scams — they sell you an eSIM that works for a month and then the company disappears. Others are legitimate but the "unlimited" claim is so throttled that it's effectively a low-speed data pipe.
So the market is a mess.
The market is a mess. And it's a mess because the underlying economics are hard. There's no magic way to make data free across borders. Every byte costs someone something. The only question is who pays and how.
So if you were building a travel connectivity setup for yourself, what would you actually do?
I'd do a three-layer approach. Layer one: keep my home carrier SIM active for SMS and as a fallback, with roaming enabled but data roaming turned off by default. Layer two: a global travel eSIM like Airalo Discover for the first day or two in a new country, so I have data the moment I land. Layer three: buy a local eSIM for any country where I'm staying more than a few days, because the local rates will almost always be better.
That's a lot of management.
It is. But the alternative is paying a premium for convenience, and the premium is still high enough that I'd rather spend the ten minutes. The eSIM makes the management easier than it used to be. You can store multiple eSIM profiles on most modern phones and switch between them in settings. You're not physically swapping anything.
What about the phones that support dual eSIM active simultaneously? That seems like it would help.
It does. The iPhone thirteen and later can have two eSIMs active at the same time. So you could have your home carrier on one line and a travel data eSIM on the other, both active, and just route data through the travel eSIM. Android phones are getting there too, though it's more fragmented. Samsung's recent flagships support dual eSIM active. That's the setup I'd recommend for someone who travels constantly.
So Daniel's SIP-first approach plus a dual eSIM phone plus a global data eSIM for gaps plus local eSIMs for longer stays.
That's the realistic answer. It's not one product. It's a strategy.
Which is less satisfying than "here's the one SIM card that solves everything," but it's honest.
The one-SIM solution is a fantasy right now. Maybe in five years, if the wholesale market consolidates and the resellers get big enough to negotiate better rates, we'll see something closer to it. But the fragmentation of the carrier market is the fundamental obstacle. There are hundreds of mobile network operators in the world, each with their own wholesale rates and their own interests. Nobody has managed to bundle them all into a single flat-rate product that works economically.
Unless you're a carrier that also owns infrastructure everywhere. But nobody does.
Nobody does. Vodafone and Orange come closest — they have operating companies in multiple countries across Europe, Africa, and Asia. But even they don't have a truly global footprint. And their roaming products still have limits.
The global roaming promise is real in the sense that the technology works, the authentication works, the billing works. You can land in almost any country and your phone will connect. But the pricing is where it falls apart.
The technology is elegant. The economics are brutal.
That's a good summary.
Let me add one more thing about the authentication side, because Daniel asked about it specifically and there's a nuance worth understanding. When you roam, your data doesn't always route back through your home carrier. That's called home routing. The alternative is local breakout, where the visited network routes your data directly to the internet. Home routing adds latency because your packets travel back to your home country and then out to the internet. Local breakout is faster but gives your home carrier less control over traffic inspection and lawful intercept.
So which one happens?
It depends on the agreement between the carriers and the network technology. In 4G and 5G, local breakout is more common. In older networks, home routing was the default. The GSMA has been pushing for local breakout because it reduces latency and backhaul costs. But some carriers prefer home routing for billing and compliance reasons.
When I'm roaming in Japan on a US carrier and my data feels slow, part of that might be the throttling, but part of it might be that my packets are traveling to California and back.
That's another reason why a local eSIM will almost always feel faster than a roaming plan. The local eSIM routes your data through the local carrier's infrastructure, with local breakout. Your packets stay in the country.
That's a practical tip worth underlining. If you're somewhere for more than a few days, get a local eSIM. Not just for cost, but for performance.
The latency difference can be substantial. A hundred milliseconds versus three hundred milliseconds. That's noticeable in video calls, gaming, anything real-time.
Alright. Let's step back. Daniel's core question was: is there a SIM that provides reliable data in most countries at an affordable monthly fee, and is that a realistic expectation? I think we've landed on: not really, not yet, but you can get close with a strategy.
The strategy is the product. The global eSIM gives you coverage on day one. The local eSIM gives you performance and price for the duration. The SIP setup handles voice independently of which data pipe you're using. And the dual eSIM phone lets you run it all without swapping anything.
The affordable monthly fee part is the hardest. The Airalo Discover global plan at eighty-nine dollars for twenty gigabytes over a year works out to about seven-fifty a month if you spread it evenly. But if you're a heavy data user, you'll burn through that in a couple of weeks. The Holafly unlimited plan at ninety-nine dollars a month is predictable but expensive. Neither is what I'd call affordable for most people.
Affordable is relative. If you're traveling for work and expensing it, a hundred dollars a month for global data is a rounding error. If you're a digital nomad on a budget, it's steep. The local eSIM approach can bring the cost down dramatically — in many countries you can get fifty gigabytes for ten or fifteen dollars. But you have to do the legwork.
The answer to "is it a realistic expectation" is: it depends on what you're willing to trade. If you want one eSIM, one bill, no thinking, you'll pay a premium and accept throttled speeds. If you want the best price and performance, you'll manage multiple eSIMs. There's no free lunch.
The wholesale roaming tariff is the lunch, and someone always pays it.
Hilbert: TP-Link Deco XE75. Three-pack. Two hundred and ninety-nine dollars.
...Alright.
Hilbert: I've got four of them in a mesh. One in the living room, one in the bedroom, one in the kitchen, one in the hallway. Eleven years I've been running my own setup. People say it's impractical, you can't do it, it's too much management. I've been doing it for eleven years.
Running your own what?
Hilbert: My own connectivity stack. I don't use carrier roaming. Haven't since twenty fifteen. I've got a dual-SIM phone, but both slots are data-only. Voice is all SIP through a PBX I run on a Raspberry Pi in the closet. When I land somewhere, I buy a local SIM — now eSIM, same thing — and I'm on the local network in five minutes. My number follows me because it's not tied to a carrier. It's tied to my SIP server.
You've been doing exactly what we're describing, but for over a decade.
Hilbert: The Raspberry Pi is the third one. The first one was an old Dell Optiplex I got from a school surplus sale. Ran Asterisk on Debian. The hard drive failed in twenty eighteen. I was in Kuala Lumpur at the time. Replaced it with a Pi three B plus. That one's still running.
And the mesh network?
Hilbert: That's for when I'm home. Which isn't often. But when I am, I want the Wi-Fi to work. The Deco units talk to each other over a wired backhaul. I ran the Ethernet through the walls myself. The landlord doesn't know.
Of course he doesn't.
Hilbert: The point is, the strategy works. It's not pretty. I've got a spreadsheet to track which eSIMs are active in which countries and when they expire. My brother-in-law thinks I'm insane. But I haven't paid a roaming charge in eleven years, and my phone number has been the same since two thousand eight.
What do you do for SMS? Two-factor codes and all that?
Hilbert: Most of them come through the SIP provider. The ones that don't, I've got a cheap prepaid SIM from my home country that I keep in a drawer. I forward the SMS to email. That's a Twilio function. Cost me about eighty cents a month.
The drawer.
Hilbert: It's a mess. There's a drawer. SIM cards, adapters, a couple of old phones, a USB LTE modem I don't use anymore. The Pi is in the closet with a UPS. The UPS battery needs replacing. I've been meaning to do it for about six months.
That's the thing about this approach. It works, but it's a hobby. You have to enjoy the tinkering.
Hilbert: I don't enjoy it. I just don't want to pay the carriers.
That's a philosophy.
Hilbert: It's a budget. I added it up once. Over eleven years, I've spent maybe three thousand dollars on hardware and local SIMs. If I'd been paying global roaming rates the whole time, it would be twenty, thirty thousand. Easy. The Pi cost thirty-five dollars. The time I spent configuring it... I don't count that.
Most people would.
Hilbert: Most people pay ten dollars a gigabyte.
The global roaming market isn't really for people like you. It's for people who don't want a drawer full of SIM cards and a Raspberry Pi in the closet.
Hilbert: The global roaming market is for people who value their time more than their money. Nothing wrong with that. But the question was whether there's a legitimate product that does what it says. The answer is yes, the products work, the technology is sound. You just pay for it. The marketing isn't lying about the coverage. It's lying about the word "unlimited."
The fair-use throttle.
Hilbert: Unlimited means you can use as much as you want at a speed that makes you not want to use very much. That's the business model.
That's about as clean a summary as we're going to get.
Hilbert: The Pi needs a new SD card too. They wear out. I've got a spare in the drawer.
If you take one thing from this, it's that global roaming works — the handshake, the authentication, the billing — it's all real and it's elegant. But the price you pay for the convenience of a single global plan is a premium on top of wholesale rates that someone, somewhere, is always paying.
The gap between the marketing promise and the economic reality is widest in that one word: unlimited. It never is. The throttle is the business model.
Thanks to Hilbert Flumingtop for producing, and for reminding us that the best connectivity setup is the one you're willing to maintain.
This has been My Weird Prompts. You can find us at my weird prompts dot com, and if you've got a question like Daniel's, email the show at show at my weird prompts dot com.
We'll be back soon.
