By Jane Wakefield BBC News Online technology staff

Sending a drunken picture of yourself to your friends may be the most popular use of picture messaging at the moment, but mobile firms are hoping to change that.

The phones that enable picture messaging are selling well - 130,000 Vodafone users and 100,000 for O2 - and are beginning to come down in price.

As picture messaging becomes increasingly popular, the mobile operators are hoping it will become as invaluable a communication method as e-mail and texting.

To this end the companies are trying to come up with a visual language for camera phones.

What's in a word?

Hurry up!

Vodafone has come up with The Little Book of Picture Messaging, which is full of ideas for how everyday objects can become significant messages.

So a door knob indicates an idiot, the back of a bus an ugly date, a thumb says "I can't come out tonight" and ice cubes are shorthand for cool.

Vodafone is at pains to point out that these are just suggestions.

"We want to get people thinking about how they can use picture messaging but we can't thrust it on the community," said a spokeswoman for the firm.

O2 has taken things a stage farther, employing a panel of academics, language experts and experts in non-verbal communication.

Grassroots evolution

Text messaging was owned by the people and evolved from the bottom up rather than corporations dictating how it was used O2 spokesman

They found that everyday language consists of two categories - social conversations for fun and communication intended to convey meaning.

In the world of text messaging, these two have been blurred.

"Texting is about saying factual things in a fun way," explained an O2 spokesman.

O2 is hoping that the same will be true of picture messaging.

"We believe it is a natural evolution from text messaging although people will probably be using it ways and coming up with a language we wouldn't have predicted," he said.

Mobile operators were late to text messaging, only providing the interconnect agreements that allowed people to chat across networks several years after the phenomenon took off.

Text messaging came from a grassroots base of customers and operators are very aware that it flourished because of this.

Any attempt to market a new phenomenon could fall flat on its face.

"Text messaging was owned by the people and evolved from the bottom up rather than corporations dictating how it was used," said the O2 spokesman.

Conveying emotion

Good luck!

This time around mobile firms are determined to lead from the front, already offering interconnect agreements and charging a premium for such services.

Initially the service was offered free but O2 has just ended its honeymoon period and started to charge 40p per message.

The price tag alone might prevent it becoming as popular as text messaging, said BT Futurologist Ian Pearson. And people might also prefer to talk.

"Text is conversational but pictures are not," he said.

The mobile operators disagree, arguing that pictures can be very emotive, especially when combined with sound clips and text.

"A girlfriend sent her boyfriend a picture of her feet in the snow with the text 'wish you were here' which conveyed a huge amount of emotion," said the O2 spokesman.

"Pictures can say more than words," he added.