European ring-tone sales were valued at 691 million euros (£548m) in 2007
Hundreds of mobile phone download sites are to be investigated after an EU-wide sweep of services.
Some 80% of the 500 websites offering ringtones and phone wallpaper breached regulations, the European Commission said on Thursday.
Unclear pricing and misleading information about what was free led to "costly surprises" for consumers, said commissioner Meglena Kuneva.
The UK regulator also wants people to receive fewer "junk" text messages.
In 2007, European ringtone sales stood at 691 million euros (£548m).
Some 495 million mobile phones are owned by Europeans.
A sweep of 500 websites - many of which targeted young people - took place across 27 EU member states, Norway and Iceland to check for breaches of European regulations.
It followed complaints from consumers who had been hit with bills they did not expect after downloading pictures or tunes on their mobile.
Results of the investigation show that 466 cases are being followed up.
Some 268 of these had some irregularities in the price, including some that did not even show the price at all. Others did not make it clear that consumers were entering into a subscription.
Some 399 failed to give complete contract details of the trader, while 344 presented information in what the authorities regarded as a misleading way.
"Far too many people are falling victim to costly surprises from mysterious charges, fees and ringtone subscriptions they learn about for the first time when they see their mobile phone bill," the commissioner said.
National authorities are now expected to contact each of the traders and have powers to fine them or close websites.
Meanwhile, mobile phone users, and parents, are being urged to check the small print of deals.
Ringtones made up an estimated 29% of the mobile content market in the EU in 2007, up 10% on the previous year.
PhonePayPlus, the regulator of these services in the UK, said that 18 million people had used phone-paid services and the UK market had grown to be worth £460m in 2007-8.
But this had also brought a growing number of complaints - more than 4,500 in the first three months of 2008.
Some included mobile phone users claiming they had been signed up for subscription services without their knowledge or consent.
The regulator has come up with a string of proposals which would mainly affect the "middle men", often operating legitimately, which work between mobile companies and content providers.
They include clear signalling of prices, for consumers to give clear approval before being signed up, and making it as easy to leave as to enter a subscription.
It also has plans for mobile phone users to receive fewer and more targeted promotional text messages.
"There is a clear lack of trust among many consumers about mobile premium services and this is small wonder when you consider the kind of harm that is being done to them by some providers," said PhonePayPlus chief executive George Kidd.
The regulator handed out fines of more than £360,000 in 2007 and has already imposed penalties of more than £390,000 this year.