Technology changes, mainly by US carrier AT&T, mean that, when travellers turn on their phones after landing, they will get a message warning them that “traditional voice calls will not work”.
The lack of traditional voice roaming means that unprepared visitors to the US will be left unable to call landline or mobile numbers – such as their hotels, car-hire companies or possibly 911 emergency services – or even friends and relatives in the US or back home. They will also be unable to receive calls.
AT&T – once part of the mighty Bell System – is advising them by text message to use “data, SMS and app-based calling”, even though international travellers have often routinely turned off data roaming because of high charges.
That means calling with apps such as Meta’s WhatsApp or the same company’s Facebook Messenger. But they can be used only between people who have also installed those apps on their mobile phones – and are prepared to pay the costs of data roaming.
And travellers need to set up those services in advance, not while waiting for a taxi or booking a hire car at a US airport.
But neither Facebook Messenger nor WhatsApp can be used to call regular landlines or even mobile customers who have not installed the apps on their phone.
Skype is one of the few apps that can be used to call regular phones, but only by users who pay an up-front fee to Microsoft, which owns the service.
This week sees the beginning of schools’ spring holidays in the UK, and German holidays start next week, meaning many families who land in US airports will be taken by surprise by the text messages from AT&T.
Customers of a number of UK-based operators, including BT’s EE, Virgin Media O2 and Three, have reported being unable to make or receive normal calls while in the US.
By this morning Vodafone UK had still not replied to an enquiry sent from Capacity last Wednesday.
A spokesperson for another operator said: “It sounds like the issue you experienced might be something to do with the VoLTE and 3G switch-off in the US.”
This person noted that some devices might not be compatible, and some device makers “had a backlog in updating its customers on this”.
Behind the changes is AT&T’s decision to retire its 2G and 3G networks – the main services that have been used for international roaming for the past 20 years – so that it can re-use the frequencies for more modern 4G and 5G technology.
Some customers find incoming calls are diverted without explanation to voicemail, but then cannot always access their voicemail services. Visitors to the US trying to make outgoing calls, whether to US or international numbers, are cut off within a second or two without explanation.
Even AT&T and the wider industry are confused about the impact of the changes.
An official AT&T spokesperson suggested on Friday to Capacity that a relatively new technology called Voice over LTE (VoLTE) will solve the problem, though many phones do not have VoLTE, which allows digital voice calling over 4G networks.
And for those with more modern phones, VoLTE roaming needs specific agreements between the person’s home carrier in Europe and that providing service in the US.
“We recently launched VoLTE inbound roaming with your carrier,” AT&T told this Capacity writer, who experienced just this problem in a number of US cities, being unable to make or receive normal voice calls in Boston, Philadelphia or Washington DC, either via regular mobile signals or via Wifi in hotels and apartments.
“The message you received upon arrival was sent in error and is only intended for carriers who do not have approved roaming capabilities with us,” said AT&T.
Yet despite this apparent agreement, this Capacity writer, a Three customer, was unable to make calls via AT&T. Capacity did not try to make test calls to the 911 emergency service while in the US, but there is no reason to think they might be an exception. It’s likely 911 calls are also blocked. In a recent change, Skype does now allow users to call 911 in the US.
An official with the GSMA, the mobile industry’s trade association, said by email: “US operators have moved quickly to migrate from 3G networks to 4G VoLTE services and it may be that the VoLTE settings on your handset had not been activated; your account has not been VoLTE-enabled by your provider; or you have a handset that is not compatible with VoLTE services.”
Most of these suggestions were incorrect, as the handset regularly makes VoLTE calls in the UK and has also done so in France.
“All of these issues would mean voice calling would not be supported on a 4G VoLTE network – but data services would still be available,” said the GSMA.
“In addition, it might be there is no 4G VoLTE roaming agreement between the US operator and your provider,” the GSMA added – something contradicted by AT&T, which said that there is a 4G VoLTE roaming agreement with Three UK.
One operator advised: “If you’re connected to 4G data service but are unable to make or receive calls or texts, it’s likely that you have a 4G capable device, but the software hasn’t been released yet, or you haven’t updated the latest software version to enable this.”
Dan Warren, now director of advanced network research at Samsung’s UK labs, was one of the people intimately connected with the specification of VoLTE a decade ago at the GSMA, where he was senior director of technology. He confirmed that VoLTE was most likely the issue.
He also received the warning message from AT&T when he landed at Boston two weeks ago. “I had all the same thoughts but also had a slightly more urgent need as I had no cash but needed to ring my hotel to summon a transfer bus,” said Warren. “My guess is it is something to do with VoLTE.”
Capacity has also talked to others left unexpectedly able to make calls when visiting the US, including the CEO of a major international carrier.
Capacity talked to Chris Lennartz, VP of mobile services product management at iBasis, one of the leading companies that the mobile industry uses to route roaming calls and messages. He’s also experienced the problem as the world opens up post-Covid: “We had people coming into the US in February,” he said. They experienced similar issues.
Operators are trying to simplify their network operations, he said, which means not running 2G, 3G, 4G and 5G in parallel. They mainly set up 2G in the 1990s and 3G a decade later, in the early 2000s.
“AT&T’s switch-off of 2G and 3G started in February,” he noted. “In some places it still works.”
Of the two other mobile networks, Verizon is also switching off 2G and 3G, but those networks were never used for international roaming as Verizon then used a standard that was incompatible with most overseas networks. Verizon didn’t even join the GSMA until 2010, when it had decided to adhere to global mobile standards and started building 4G.
T-Mobile US, owned by Deutsche Telekom, “is switching off 3G in October, but not 2G,” said Lennartz. Technically adept visitors might be able to force their mobiles to roam onto T-Mobile in the US, he suggested. A visitor’s home operator might refuse to authorise such as connection, he warned.
A spokesperson for a European operator said customers left unable to make calls should “manually search for the other provider (T-Mobile) to connect to all 3G services”.
However, at iBasis, Lennartz said that a non-US phone will normally start by finding a 4G data connection on AT&T, but then fail to find a 2G or 3G service for voice on the same network.
iBasis is looking for a workaround, said Lennartz. “With a bit of wizardry we could make it work.”
However, because international VoLTE calls – even when they work – are all data-based, and tunnel through the global mobile system, there is no inbound revenue for calls. Operators “miss a lot of the revenue”, he said: the implication being that there is no financial incentive for operators to make global VoLTE roaming work.
“It’s a very precarious situation, but AT&T is doing all they can,” said Lennartz.
The GSMA said: “The sunsetting of 3G networks is not as advanced in Europe as it is in the US, which in turn, means VoLTE is not as widely used for voice services. It should be noted that this is not a compliance issue, but a business decision based on the priorities for domestic customers.”
But it’s a decision that can take thousands of international visitors to the US by surprise – and the next few days will be the first time most of them find out.
