EE, Three, Vodafone customers face having to pay £120 after summer holiday

A survey of 2,000 mobile phone users recently found 58 per cent are puzzled about how they will be charged, whether it's a daily cost or a cost per gigabyte they use. This confusion has led to 59 per cent paying an average of £24 for using their phone abroad on a single trip. However, one in 20 (four per cent) have been hit with a bill exceeding £120.

Networks who charge include EE, Sky, Three and Vodafone. Just 11 mobile networks will still let you roam for free, including Asda, which lets you roam in 46 countries but with a limit of 5GB and anything over that being charged at 10p per MB. Asda says it will alert customers when they reach 80% of the limit, and also when all 100% is used.

BT Mobile’s ‘Roam Like Home’ lets customers roam for free in 47 destinations and users can use your mobile plan allowance to use data, make calls and send texts back to the UK as well as to receive calls and texts for free when you’re roaming in these zones.

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GiffGaff plans can be used in the EU and some other destinations at no extra cost. And there are no roaming charges with some Lebarara and iD Mobile plans. O2 customers, meanwhile, have been told the provider won't bring back roaming charges for the European Union zone, with a fair usage cap of 25GB. Plusnet, like BT, has a Roam Like at Home tariff. Tesco Mobile and Talkmobile have free EU roaming too, and Smarty too.

Simrat Sharma, a mobiles expert at Uswitch, said switching to an eSIM - short for embedded SIM - can be cheaper than using international roaming. “eSIMs make it easier to change networks," she said. "So for example, if you’re abroad you can quickly connect to the local network to pay local rates - without having to add or swap a physical local SIM card for your device.

"This means travel eSIMs are almost always cheaper than using international roaming, as users are effectively tapping into the same network plans as locals. If you’re regularly switching numbers or travelling to different locations, you’ll be able to keep them all safely in digital format rather than carrying around a number of small cards.

“The software can easily be accessed via your device’s app store and uploaded to your phone in a few quick steps."