Here’s an idea that’s equal parts compelling and frightening: a presence service that is integrated not with a instant message client, but with your mobile’s contact book.

A presence service is the bit of an Instant Messaging (IM) application such as MSN, AIM or Yahoo Messenger that makes it possible to see which of your buddies is online, usually with a mood message thrown in (“bored”, “working from home” etc.).

It is what makes IM so compelling, to the point that many kids think email is just for old people (ars technica). Mobiles, of course, are not so stratified by age, but a quick glance in any public place in Western Europe will demonstrate that the under 25s are particularly attached to theirs. Hence the notion that tying presence information to a mobile’s contact list could prove to be very popular indeed with that crowd.

As befits the place, a couple of Finns have had that brainwave, and are now busy implementing it in, you guessed it, Nokia phones (Jaiku). More than that, they’ve clocked that a mobile can show much more “social peripheral vision” than simple presence online: it can also show location.

Once you’ve got that, you can let your imagination run riot. No more “I’m on the train” type conversations, because your mate can simply see that before even calling you. You could see how close, physically, your mates are to you when you look for them in a busy place. You can also see where all your mates are at any given point- like, all together, but not with you. And since these are mobiles, not PCs, even not seeing someone online can become quite significant.

With most modern tech, there’s usually a period of grace before abuse starts happening and rules are required. Think email before spam, or the web before people figured out how to make money on it. With this one, even the pioneers are keenly aware of the massive potential for abuse and a possible need to put some limits on the technology.

It might still prove too compelling to stop, though.