Football fans heading to this summer's European Championships have been warned they risk racking up huge mobile bills in Ukraine.
As the country is not part of the European Union, users will pay much higher rates than in the rest of Europe as calls, texts and internet browsing will not be subject to price caps.
The Euros, which start on 8 June, take place in Poland and Ukraine. Poland is in the EU so fans will get cheaper calls there.
All England's group games are in Ukraine, where a possible quarter-final will also take place if Roy Hodgson's team qualify.
A potential semi-final could be in Poland or Ukraine, with the final in the Ukrainian capital, Kiev.
Price comparison site uSwitch.com, which issued the warning, says fans risk £35-a-day mobile bills by making and receiving two five-minute calls, listening to a two-minute voicemail message and sending five text messages and one photo message.
What's more, 1MB of mobile internet data, which can easily be used in one browsing session, costs an average of just over £6 in Ukraine across the five main UK networks.
Travellers can avoid this charge by using the internet and apps which support the web in wi-fi zones.
It is also wise to switch off the data roaming function (which allows you to browse the internet overseas) unless absolutely needed as many apps use data in the background.
O2 customers, for example, in Ukraine will pay £1.20 a minute to make a call, 85p a minute to receive a call, 40p to send a text and £6 per MB of internet data.
According to uSwitch, O2 and Vodafone are the only networks that place an automatic cap on data usage worldwide for pay monthly customers.
Within the EU, calls made are capped at 35p per minute, incoming calls at 11p per minute and texts at 11p. Providers mustn't allow users to spend over about £42 unless they opt out of that cap.
These caps will fall from 1 July, the day of the Euro 2012 final.
Becca Talbot, MoneySavingExpert.com consumer products analyst, says: If you're going to make many calls home and send texts while abroad, it may be worth getting a pre-paid international Sim card. These can offer rates of as little as 50p/min to call back to the UK from Ukraine.
"These will only work in unlocked handsets, though. So if your phone isn't already unlocked, paying to get it unlocked could negate any savings you'd potentially make."
Ernest Doku, from uSwitch.com, says: "Footie fans have to think ahead if using their phones while following England.
"The first thing England fans going to Ukraine – or indeed anyone taking a holiday outside the EU – should do is talk to their network. They may be able to advise you of a bundle, or at least let you know the costs involved with using your phone abroad."