By Mark Ward
BBC News Online technology correspondent
Carrying a mobile phone? Then someone could be tracking your every movement and know where you are. Big Brother? Perhaps, but it could just be a Mexican restaurant wanting to invite you in for dinner.
Location-bases services look set to take-off
Your mobile phone says a lot about you.
The type of handset you own, the fascia you choose for it, the ringtone, even how quickly you answer it are good clues to how you think of yourself.
But soon your mobile phone could be saying a lot more about you and your lifestyle as handsets evolve into devices that know where they are and share this information with almost anyone that wants to know it.
"All the big four operators now offer a commercial service so you can send them a telephone number and they will tell you where it is," said Colin Bates, chief technology officer at location services company Mobile Commerce.
For years many companies have dreamed of using handset location as the basis for a range of services that let you know such things as the position of the nearest cashpoint, pub or Mexican restaurant.
Before now network operators have offered these services to their own subscribers and few others.
But location-based services are going to be much more common, now that locations can be requested for a few pence a time and firms such as Mobile Commerce and Verilocation are springing up to funnel location requests to the various networks.
The location system works best in urban areas covered by lots of base stations that have overlapping coverage. This lets operators give a location fix accurate to about 200 metres.
In rural areas the accuracy worsens because there are fewer base stations to use as a guide to a handset's location.
Already location maps are pretty accurate
"It is not as precise as the global positioning system, but it is good enough," said Mr Bates.
He said that the advent of cheap, location look-ups would kick off a huge range of uses that have previously been too expensive or fiddly to do.
Among the first users will be firms with fleets of vehicles that want to keep an eye on where their deliverymen and salesmen are going all day, said Mr Bates.
But it is likely that the biggest use of location services will be for consumers out and about in towns and city centres.
Family and friends
Already trials of location-based services based around discrete locations, such as out of town shopping malls, have shown that they are effective. Restaurants have filled empty tables and shops have tempted consumers by sending them text messages when they know they are near.
A report out this week by think tank Demos said that location services could be the "killer application" for future third-generation phones.
Demos believes that when phones can easily talk to other devices and maintain contact with the handsets of your friends so you always know where they, it will spur a huge take-up of such services.
Futuristic services could be tied to the buddy lists many people maintain on instant messaging systems that let you know when your mates are close-by so you never miss them.
They could even help the government realise its ambition to introduce per-journey charges for drivers, instead of a flat-rate road tax.
But you may not have to wait until 3G phones are widely available to get such services.
Location services could boost the takeup of road charging
Verilocation is already operating a web-based system that instantly produces a map of a handset's whereabouts.
Subscription to the service is costly, but you can even try the service for yourself once for free.
Andrew Overton, managing director of Verilocation, said currently most of its users were firms keen to track the movements of staff via their handsets, but in the future it would be pitching services to consumers.
Soon Verilocation plans to offer a service for families that lets worried parents find out where their offspring are. The service will cost a fixed amount every month and let family members check locations a few times per month.
Mr Overton said Data Protection legislation means that tracking cannot be done without consent of a handset owner.