Europe's mobile phone operators have been warned they must cut the cost of texting and internet access for users who are overseas or face regulation.
The cost of calling from abroad has become much cheaper
EU Commissioner Viviane Reding said firms have until 1 July to slash their so-called "roaming" charges.
A text sent while abroad can cost as much as 49 pence ($0.95) and a study found that transferring 1 megabyte (MB) of data on average costs £4.11.
Mobile phone companies say they have already begun cutting prices.
"Sending text messages or downloading other data via a mobile phone while in another EU country should not be substantially more expensive for a consumer than sending text messages or downloading data at home," Ms Reding said.
"If the industry does what it claims it can do, bringing prices down to normal, then of course, regulation will not be necessary," she added.
The Commissioner called for "credible reductions" to fees charged to business travellers and holiday makers before the summer deadline.
She warned roaming charges of anything more than about 2 pence above domestic texting charges would be unacceptable.
Last year the EU adopted regulations proposed by the EU Commissioner that forced mobile phone companies to lower the costs of making calls for customers outside their home country.
On average those charges were halved.
But the price cap does not cover mobile internet or the 200 billion text messages that are sent a year in western Europe.
The new generation of phones have made it easier to surf the internet and email, but it is still an expensive option.
"Roaming the internet abroad has so far been treated as a businessman's perk which companies will pick up the huge bill for," said BBC Technology Correspondent, Rory Cellan-Jones.
"But it is becoming a big consumer thing and consumers are getting cross about how much it costs."
The mobile phone industry said costs are coming down quickly, particularly for mobile internet access.
"Accessing the internet and web pages while you're roaming around Europe using a mobile phone can be expensive," said Tom Phillips, head of Government and Regulatory Affairs at the GSM Association.
"But it's a very new service, it's growing in popularity and the prices are coming down very quickly."
Ms Reding was cautious about interfering in the data downloading market, which is still in its infancy, but urged mobile phone operators to alert customers to their charges to avoid "shock bills".