Advertising on mobile phones is a tiny business. Last year spending on mobile ads was $ 871 million worldwide according to lnforma Telecoms & Media, a research firm, compared with $ 24 billion spent on internet advertising and $450 billion spent on all advertising. But marketers are hailing the mobile phone as advertising's promised land. It is destined, some say, to replace not only internet advertising,the latest fad, but also television, radio, print and billboards, the four traditional pillars of the business.

The 2.5 billion mobile phones around the world can potentially reach a much bigger audience than the planet's billion or so personal computers. The number of mobile phones in use is also growing much faster than the number of computers, especially in poorer countries. Furthermore, most people carry their mobile with them everywhere—something that cannot be said of television or computers.

Yet the biggest selling point of mobile ads is what marketing types call ' relevance' . Advertisers believe that about half of all traditional advertising does not reach the right audience. But mobile advertising through text messages is the most focused: if marketers use mobile firms' profiles of their customers cleverly enough, they can tailor their advertisements to match each subscriber's habits.

In September, Blyk, a new mobile operator, launched a service in Britain that aims to do just that. It offers subscribers 2]7 free text messages and 43 free minutes of voice calls per month as long as they agree to receive six advertisements by text message every day. To sign up for the service,customers must fill out a questionnaire about their hobbies and habits. So advertisers can target their messages very precisely. ' Britain is the largest, but also the trickiest European ad market, so if it works here it will work everywhere,' says Pekka Ala-Pietila, chief executive and one of the founders of Blyk. Customers are rewarded in return for text message advertisements on their mobile phones.