Telecoms watchdog Ofcom has set out an action plan to tackle the issue of "bill shock" where mobile phone customers on contracts are surprised by unexpected costs in their bills.
The regulator identified the main causes for people to be taken unawares when receiving their bill as being when they have downloaded data without realising the cost, often when outside the EU, exceeding allowances when calling other mobiles or calling numbers outside of allowances, and when their phone had been lost or stolen.
Ofcom's proposals follow a review into the causes of bill shock in the communications sector, which found that mobile phone contract customers were the most likely to be affected by the problem.
Research conducted as part of the review revealed that as many as 1.4 million customers may have been affected in the past six months.
Ofcom said it will now work with the mobile phone industry on a series of measures to address the main issues identified by the review.
It wants to encourage companies to set financial caps on mobile phone usage, explore whether they can limit the amount customers are liable to pay if their phone is stolen, make their tariffs more transparent and increase customers' awareness about the issue.
The watchdog is also supporting proposals to extend EU roaming regulations worldwide to protect customers travelling further afield.
Marzena Lipman, digital policy manager at Consumer Focus, welcomed the announcement.
She said: "Massive mobile bills when people return from trips abroad are the last thing they need.
"Ofcom's proposals to tackle this issue are very welcome, particularly moves to extend protections to customers travelling further afield to non-EU countries.
"The next logical stage would be to also protect mobile phone customers in the UK.
"Consumers travelling in Europe are protected from unexpectedly high bills with a 50 euro (£42) cut-off limit, consumers in the UK should be entitled to similar levels of protection.
"While some customers may want a higher data allowance, an opt-out default cut-off limit could help end bill shocks in the UK."
Which? executive director Richard Lloyd added: "Ofcom's report confirms what consumers have been telling us for years - that bill shock is a big problem with as many as 1.4 million mobile phone customers affected in the last six months alone.
"We want clearer information for customers from the phone companies about what they charge for services in the UK and abroad, plus greater protection for consumers from hefty data charges.
"Ofcom must stand by its promise to investigate data roaming measures in the UK if EU negotiations fail and we want to see more pressure put on UK operators to adopt data caps and spending alerts."