Communications regulator Ofcom announced on Tuesday that it has begun examining the mobile roaming fees that UK mobile users must pay when they use their phones abroad.
The investigation into the UK's wholesale mobile roaming market is part of a Europe-wide inquiry into the issue. It comes amid growing concern that consumers are being overcharged when they use their mobile phones to make and receive calls and text messages while travelling abroad.
"International roaming agreements are complex and wholesale charges between network operators can vary significantly. This has led to confusion among users at the wide range of prices they might pay. Although some operators now offer simpler, unified retail tariffs, some consumers still incur substantial mobile phone bills as a result of international roaming charges," said Ofcom in a statement.
Ofcom has also published a guide on its Web site to help people avoid running up hefty bills when using their phone abroad.
Vodafone, one of the UK's five mobile operators, said it welcomed Ofcom's move, even though the regulator could eventually force operators to cut their prices.
"It is vital for consumers to understand what they are paying when roaming abroad and we have been working hard to provide our customers with better value and greater transparency with Vodafone Passport," said Phil Kirby, director of regulatory affairs for Vodafone UK.
With Vodafone Passport, users can use call minutes from their domestic subscription abroad, plus a 75p fee per call on top.
Ofcom's investigation will be restricted to mobile phone calls and messages, and will not cover data services. As ZDNet UK reported last autumn, some operators are imposing excessive charges on customers who use 3G and GPRS datacards overseas.
One Orange customer was charged £800 after using his datacard to download just 80MB of data in France and Germany.
An Ofcom spokesman explained that data services would not be investigated at this stage, because such services are relatively new.
"Ofcom's best estimate is that only around 2.5 percent of UK operator's revenue is generated through accessing such services in the UK... given that the development of mobile data and internet services is at an early stage, Ofcom does not intend to consider these services within its review. The focus is on voice and SMS services which make up the majority of consumer usage, particularly whilst abroad," said the Ofcom spokesman.