Remember when mobile phones were simply for talking to people? Here’s yet another fashionable use for them to add to video camera, music player, satellite navigator and tea-maker. Cellphones are now a tool for pinning virtual messages to physical places, messages that any passing stranger can retrieve once their phone comes in contact with the location-based "tag". It’s all part of a trend to map out the geographical world with digital information held on the internet, building what the techies call "the geospatial web". Geospatial what? Guys, we can’t use jargon like that in The Times Magazine. Can’t we just call it "place-tagging"?

Let’s say you want to recommend a local pâtisserie to tourists, or just let friends know you’re in the neighbourhood. Simply "tag" the location with a code designed to deliver a message by phone. Some techniques use the Global Positioning System to make phones respond to a place, others rely on visitors sending texts or e-mails to addresses scribbled on to pavements. So far, only a few thousand people have been leaving virtual calling cards, but the trend offers so much scope for social networking – not to mention advertising – that we predict you’ll soon be hearing much more about it.

Up to now, creativity not commerce has been driving the trend. Take the yellow arrows that you may have seen stuck on to lampposts and street benches from Bangor to Dungeness. Part of a "global public art project" co-ordinated at yellowarrow.net, the stickers let anyone with a phone share their thoughts about a place with passers-by. Each arrow comes with a unique code, which the person placing the sticker sends by text to a central phone number along with their personal observations. Any subsequent visitor merely sends a text containing the code to receive by return the original note with which the place was tagged. In London, arrows currently recommend "a quiet garden" in a Camden pub and "the best Lebanese takeaway" in town. Just don’t ask whether placing stickers in the street without permission is entirely within the law.

Another project, Grafedia (www.grafedia.net), suggests hand-chalked e-mail addresses as an alternative. Spot a blue underlined phrase on an object in the street, and, with a late-generation phone, e-mail the phrase with the suffix "@grafedia.net". By return, you’ll receive a message in the form of text, video or sound file, depending on how the tagger chose to personalise the location. "Every surface becomes potentially a web page," the New York-based team behind Grafedia explains, "and the entire physical world can be joined with the internet."

This is just the start. If you want a collaborative, up-to-date travel guide, point your cameraphone to the barcode-like tags starting to appear on landmark buildings. These are "Semapedia" tags (semapedia.org), which link the place to its entry in the Wikipedia online dictionary. To leave messages hovering in mid-air for strangers or friends to pick up, a program called Socialight (socialight.com) will tie that data to your phone’s physical co-ordinates and make it available to others when their phones move into proximity. Siemens, meanwhile, is developing a service it calls "digital graffiti" that will let advertisers join your friends in sending you location-aware text messages. That’s the trouble with living in the real world. You know that sooner or later it will become just another quirky byway of the internet.

david.rowan@thetimes.co.uk

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