Rules on ringtone ads are being beefed up following a deluge of complaints to watchdog that regulates premium rate phone services in the UK.

Icstis has welcomed the new safeguards to protect consumers signing up for premium rate subscription services, such as ringtones and wallpapers.

It says misleading ads have meant many people have run up large bills because all costs are not spelled out.

More than 100 people complained to the watchdog about the Crazy Frog ringtone.

'Teenagers vulnerable'

The new rules were draw up by the UK's mobile phone operators to determine how premium rate subscription services are marketed by content providers.

The deadline for complying with them is 30 August.

The rules go as far as to dictate font sizes and how prices should be displayed in TV adverts.

In recent months, many people have mistakenly run up large bills by inadvertently subscribing to ringtone and text services when they thought they were just buying one tune.

The popularity of the Crazy Frog ringtone has led many people to download it to their phone without realising that it is only part of a bundle of tunes they will regularly be billed for.

"Teenagers are particularly vulnerable as they do not always fully appreciate the conditions attached to such services," said George Kidd, Icstis director.

The wildly popular Crazy Frog has made history by becoming the first ringtone to reach the top of the pop charts.

It is part of a package of ringtones created by mobile content company Jamster, and sold through a mobile service provider called MBlox.

Consumers who may think they are buying the Crazy Frog ringtone are signing up for a subscription plan.

Each week, they receive a new text message for which they are charged £3, enabling them to download another ringtone.

No small print

The new rules, drawn up by mobile operators and backed by premium service watchdog Icstis, will force content sellers to make it clear what people have bought and how much ongoing costs are.

They demand that details of prices and how often people are billed are prominent in adverts. For TV adverts, scrolling price banners and small fonts are outlawed.

In print, adverts prices and conditions must be in the main body of an advert rather than the small print.

They also stipulate that as soon as someone has signed up for a service they are sent a text message telling them what they are getting.

Customers must also get a reminder of how to unsubscribe every month or every time £20 is spent.

Mr Kidd said the rules built on the universal "stop" command that was introduced in 2004. This lets people unsubscribe by sending the word "stop" to the short code associated with the service they have signed up for.

Adrian Harris, founder of the Grumbletext website where people log problems with phone services, said he welcomed the new safeguards up to a point.

If all firms complied with the rules then consumers would definitely be better off, he said.

But, he said, the big problem was policing ringtone sellers. He called on Icstis to be more active in seeking out offending firms rather than just investigating on a case-by-case basis.

At the end of June the Department of Trade and Industry announced a big increase in fines for firms that break rules on the selling of premium rate phone services.

After the increase the maximum fine is £250,000 - more than double the previous upper limit of £100,000.