You step off the plane in a different country, and your holiday can finally begin. Ever wondered how the first text you send makes its way back to the UK?


The temperature’s balmy, your sunglasses are on and you’re ready for 10 days on the beach. But before the relaxation properly starts, you step off the plane and turn your phone back on to tell people you’ve landed safely. What’s going on behind the scenes? And how does your text message make it home?

We wanted to find out how the journey works, so we’ve tracked down Vodafone’s resident roaming expert Alberto Morales for the inside scoop.

600 handshakes

Alberto explains that a comprehensive set of roaming agreements is step one for any network operator: “If we want this to work we need a roaming agreement. That’s a commercial agreement between Vodafone and operators around the world, which opens up signalling routes.

“When you’ve got a bigger global footprint, things become easier to manage.”

“We’ve got to pay other operators a certain amount of money every time a call or SMS goes through their networks,” he adds. “They charge us because we’re using their resources, but the roaming agreement helps structure that payment.” Sometimes we have to use several networks to get somewhere, too – a bit like passing something down a line of people.

The more agreements we have, the more places we can provide signal, but it helps that Vodafone’s got size on our side…

“What we’ve got that works in our favour is that Vodafone is a big group around the world, and therefore we’ve got a lot of infrastructure that’s our own. That makes things easier in terms of attaining a high quality of service.

“Vodafone is in more than 25 countries,” says Alberto, “and when you’ve got a bigger global footprint, things become easier to manage. But on top of that, we have more than 600 roaming agreements around the world.”

Born to Server 


Ok, so we’ve got the routes between countries sorted. But what’s actually going on when you use your phone? Alberto reveals that the system revolves around a complex set of servers that push information back and forth at lightning speeds.

“When you turn your phone on in a foreign country, your phone looks for signal from nearby operators,” Alberto explains. “It receives signal from the different antennas around it, and it selects one of those operators depending on the power and strength of the signal, and proximity of the nearest base stations.”


Once your phone locks that down, it needs to gather some information about you. There are two databases to remember here – the Home Location Register (HLR) and the Visitor Location Register (VLR). Every network has several of each in every country and, put simply, the VLR’s job is to ask the HLR who you are:

“The VLR asks our HLR, which is a database in the UK, to retrieve all the information related to you. Can you call from abroad? Can you browse? Do you have any barring? – That sort of thing. Once the foreign operator (which may well be an international arm of Vodafone) has got that information, it considers the phone as authorised to use the network. The moment you can see the network on your phone’s screen, you know you’ve been identified.”

Fire away!


The HLR has told the VLR who you are, and you’re all good to go. You tap out a text and press send. What’s next?

“Text messages use a server called SMSC (Short Message Service Centre). When you send a text, the first thing it’ll do is tell the VLR (with which you’re now authorised) whether you’re a Vodafone UK customer. After that, the SMSC will ask the HLR to find out where the phone you’re trying to text is located.

“It’ll say it’s registered in the UK, for example, and then it’ll be able to send the text to that person’s HLR, and then on to their phone.” If the number you’re trying to reach is also abroad, the SMSC will fire it to the VLR that they’re connected to, and then from the VLR to their phone.

Got that? Essentially, the SMSC, the HLR and the VLR all talk to each other with a series of instant checks to make sure you’re allowed to text, and to find out where the person you’re texting is.

“Your SMSC address is stored inside your phone,” says Alberto. “If you buy a phone from Vodafone UK, the right SMSC address is stored in the handset – so that when you send an SMS, it’ll automatically go to your SMSC.”

EuroTraveller explained

Wherever he goes, James is armed with a selection of smartphones

When we’re connecting your phone in different countries, we have to pay those networks for using their VLRs and other parts of their infrastructure. There’s extra costs involved here, and that’s why it’s generally a bit more expensive to text, call and browse the web when you’re in a different country, but that’s something we’ve tried to make less of a headache with EuroTraveller.

What’s the deal? Simple: access your normal tariff allowance when you’re away for a fixed price. Vodafone’s Roaming product specialist Vincent Hache explains:

“You don’t have to worry about the fact that you’ve used this much internet here, and sent a text there, etc.”

“If you’ve already opted into EuroTraveller, you’ll pay £3 each day once you’ve either sent a text, made a call, or started using the internet, and you’ve then got the freedom to use your UK minutes, texts and internet like you would at home.” We deal with the complexity on our side, so you won’t see any sporadic, ad-hoc charges on your bill.

“That way,” says Vincent, “We’ve got a consistent way of explaining what you’ll pay, so you don’t have to worry about the fact that you’ve used this much internet here, and sent a text there, etc., or worry about trying to add up what all that costs.

“The technical process for EuroTraveller is the same,” he adds, “and what Vodafone is paying to the other networks is the same. The difference is from a billing perspective for you as a customer. We remove the complexity by removing the charges that are based on what you’re doing, and try a broader approach.”

All caught up? VLRs, HLRs, nodes, servers and data routes; it’s all complex stuff, but it’s how we connect you to your friends and family around the world. For more information and terms on EuroTraveller, click here.

Any questions? Drop us a line via the comments section below. If you need a bit of advice about keeping your mobile safe while on holiday, check out Ofcom’s new guide.