In theory, advertising agencies should love mobile telephones. What better way to reach consumers on the go?

In practice, though, advertising industry executives are growing increasingly concerned that the popularity of mobile telephones will only make their jobs harder. Their worries centre on the impact that mobile phone use is having on the social lives of young people. They fear the phones are creating a new, more furtive generation that will be more difficult to reach with traditional advertising.

?I think loyalty is definitely an issue with this audience,? says Jean-Paul Edwards, head of media futures at Manning Gottlieb OMD, a media-buying and -planning unit of Omnicom, the world's largest marketing services group. ?They are more fickle . . . less entrenched in their habits.?

Behind the scenes, ad agencies are furiously studying the habits of the mobile phone generation. The results so far have proved disconcerting as Mr Edwards's company discovered when it asked people in the UK aged between 15 and 24 to go without mobile phones for two weeks and record their experiences.

Several of the young people deprived of their phones found they had to engage in a novel form of social interaction - talking to their friends' parents. It seems that previously they had arranged meetings at other locations, using mobile phones to keep in contact. What for previous generations had been a rite of passage calling on friends at their homes had become an anachronism.

?They never go into the house. They never meet the parents,? Mr Edwards says. ?They are empowered by this device to avoid situations they don't like, like meeting a friend's parents.?

The fear among advertisers is that they will meet a similar fate and wind up being ignored by the generation that has grown up using mobile phones. The young always have been self-involved, but never quite like this.

The mobile phone ?is the ultimate expression of an individualistic society, which I think is the thing worrying everyone,? says Dan O'Donoghue, strategic planning director for Publicis, the marketing group. ?We are all becoming so individualistic we have no relation to society.?

A study of 1,600 young Europeans this year by Omnicom's BBDO ad agency detected similar tendencies, describing the continent's youth as pursuing what it called a ?me project?.

The study found that young Europeans craved new experiences but distrusted large organisations and national obligations. Only 38 per cent said they would fight for their country.

?The rest of the world may have problems but they rarely feel overwhelmed by the complexities of modern life,? the study said. ?They simply shut out what doesn't affect them.?

These developments do not necessarily spell disaster for every advertiser. For instance, the lack of loyalty Mr Edwards noticed could help new brands fight entrenched competitors. Viral campaigns intended to create ?buzz? around a product will benefit because mobile phones give young people a chance to maintain more relationships and seek out more opinions.

Advertising executives stress that they are only in the early stages of putting mobile phones to work as a medium for marketing messages. One idea gaining currency is using phones to hand out ?mobile coupons? bar codes sent in text-message form that would entitle consumers to discounts at stores.

But whatever progress is made in these areas, advertisers will still have to tailor their messages to the personality types emerging in the mobile-phone era, agency executives say.

Already, creative campaigns for products such as Sony's PlayStation are running for shorter periods as a way to maintain the interest of young people, Mr Edwards says.

Valerie Accary, managing director for multinational clients at BBDO Europe, says her study suggests young people like brands that give them ?new experiences all the time?. The imp-lication is that ad campaigns must surprise to succeed.

Churning out all these advertising campaigns and constantly retooling brands will be hard work for marketers and could put pressure on their profit margins.

But there appears to be little alternative. Advertisers will have to keep moving if they want to reach young people who no longer knock on the front door but wait at the corner, playing with the keypads on their mobile phones.