Revered by teenagers, relied on by executives, and a lifeline for the lost or lonely-mobile phones have reached new levels of intimacy. Dressed in its own designer outfit and given a carefully chosen ring tone, its signals follow people wherever they go.

For a piece of technology to achieve such a close and personal relationship with its owner is quite extraordinary. Mobile operators cannot ignore the fact - they must respect the intimacy and ensure that the phone reciprocates its owner's love.

"Personalisation and mobile phones go hand-in-hand. People are always looking for how to make their mobile cool and sophisticated," says Reza Chady, head of global market research at Nokia. "To get the most out of the services on offer the content and delivery should be personalised too."

Perhaps one of the greatest drivers for personalisation on mobiles is the size of the screen. Thus, there is a premium on displaying exactly the right content to customers. Furthermore, people tend to use their mobiles in distracting environments, so navigation through a site, or menus, must be simple and minimal.

Many devices already incorporate predictive text capabilities. The phone learns words its owner frequently types and suggests them to the user to save laborious button pushing. Adaptive menus also come into their own; frequently-chosen menu options move to the top of the list.

A platform developed by Logica Mobile Networks identifies devices and intelligently renders content to fit their screens. It cuts out pictures and reformats text according to the device and on which it appears.

The mobile industry faces a daunting challenge, for personalisation must pervade every level of mobile technology, from handsets to homepages. On the web, the emphasis on personalisation is to deduce customer' interests and push out appropriate marketing. On mobiles, by contrast, personalisation must slim everything down to the bare essentials.

For a start, mobile owners will not tolerate "spam" or adeluge of unwanted information, though that does not mean that mobile marketing (m-marketing) is impossible. Research by Nokia shows that customers believe that m-marketing and advertising is inevitable; a significant majority of mobile users even said they would welcome some advertising messages, as long as they were relevant and could be switched off easily.

In a Finnish trial, volunteers registered to get discounts at Nokia's Promo shops. Five different m-coupons were sent out via SMS, including straight 10 per cent discount offers and special lunchtime deals.

Nokia identifies four principles that operators should follow if considering m-marketing: choice, control, customisation, and quid quo pro - giving customers something in return for receiving adverts, such as discounts or reduced tariffs. Young people especially are more likely to accept advertising if it saves them money.

Many companies involved in mobile personalisation advocate adaptive personalisation. These use artificial intelligence techniques to monitor a user's behaviour, analyse their tastes and deduce the most appetising marketing and content to deliver.

There are two major advantages with implicit profiling of users. First, there are no forms for the user to fill in - a cumbersome operation on a mobile device and inconvenient if it has to be done via the web. Furthermore, tick box options for personalised content rarely enable highly personalised services.

Second, while it is relatively easy to filter content depending on preferences, prioritising it more of a challenge. Only clickstream analysis can discern content usage ranking content accordingly.

"Ultimately, accurate profiles will govern how much 3G operators and content providers can charge third parties for adverts and promotions," notes Nick Bidmead, chief executive of NCorp, a personalisation technology developer. "For example, if you understand when people go on holiday, whom they go away with, how much they spend and where they prefer to go, then you are maximising the take-up rate of any personalised advert or promotion. And if such services are accurate, then they will be well-received by the end-user and not treated as spam."

Nevertheless, Nokia's Reza Chady strongly recommends the four essentials of m-marketing. "In terms of personalisation, mobile marketing is an emotive subject. Service providers have to get the balance completely right or else m-marketing will be intrusive and upset the user."

The only sensible option is to keep the user in full control, says Tony Rubin, chief executive of Rocking Frog, a business based within BTexact Technologies' corporate incubator, Brightstar. Working with BT Wholesale, Rocking Frog has developed a wireless application that allows users to personalise news, travel and entertainment information via SMS, internet and voice channels. It combines intelligent learning and user customisation.

"When users register for the service they are asked a number of questions to build up their initial profile. The technology then observes and learns what you find most relevant," he says.

If a user has expressed interest in Manchester and Arts, for instance, but only ever uses information on theatres the system may ask if you would like to update your profile to send events updates specifically on Manchester theatres. But unlike other implicit profiling techniques, the Rocking Frog technology ensures that users can always edit their profile.

Mobile personalisation can go a whole lot further, however, by taking context and location into account. Using location-based techniques, information can be made geographically relevant too. An Edinburgh businessman on a trip to London can locate not just the nearest restaurants, but also ones that suit his palate - Chinese but not Szechuan, for example. "It's about delivering to people's motivations," says Mr Rubin.

Mobile operators believe that location-based techniques will work best in entertainment and telematic services. In one seamless service it may soon be possible to receive turn-by-turn driving instructions and traffic updates to a destination, then be told what amenities are in the area of interest to you. Even the location based m-coupon, sent to your handset when you pass a shop of interest, does not seem outlandish. According to a Nokia report, in the next five years, location-sensitive notifications and alerts will achieve 27 per cent and 35 per cent penetration in Western Europe and the US respectively

Relationships form the core of these new mobile services. Customers must never feel betrayed by mobiles; mobile operators ultimately take responsibility for the future happiness of our marriage to the mobile.

"The end-user wants the operator to play a guardian role," says Mr Chady. "Operators must build on the strong relationship they already have with customers to encourage them to opt into these new services."