LONDON - Mobile operators in the UK have joined forces to protect children from adult content accessible on mobile phones.

Orange, O2, T-Mobile, Vodafone, Virgin and 3 have signed up to a Code of Practice, which imposes an "18" classification on adult content.

E-commerce Minister Stephen Timms said it was a much-needed "excellent example of responsible self-regulation".

It covers images, video, gambling, games, chatrooms and net access but not premium rate voice and SMS services.

They will still be regulated by the ICSTIS (Independent Committee for the Supervision of Standards of Telephone Information Services) Code of Practice.

Mobile operators have been working on a framework to control and censor the distribution of mobile content over the last 12 months.

It means content with an 18 certificate will only be available when the network operators verify the age of the user.

An independent body will decide on standards for the classification system and will work in a similar way to other parts of the media industry.

Children's charities welcomed the step, but said they hoped those operating similar services through fixed-line net would do the same.

"These new measures are a great step forward for the mobile phone industry and we very much welcome them," said John Carr, net advisor for NCH.

"The new code is going to make many people ask why, if the mobile people can do it, the fixed internet people can't.

"We are calling on them to take this forward as a matter of urgency," he said.

With newer 2.5G and 3G mobiles that have colour screens, video and mobile surfing, there has been a growing concern about how much inappropriate content children have access to from their pockets.

Chatroom access through mobiles have been a particular concern, as they are popular with many children and teenagers.

The code will ban those under 18 from mobile chatrooms which are not moderated, in an attempt to protect children from online grooming.

Mobile chatrooms - or Wap chatrooms - are similar to net chatrooms, but involve groups of people sending messages which all those in the same room can read on their phone screens.

Mr Carr said children's charities would be closely monitoring how the guidelines worked in practice and reviewing its effectiveness.