GPS Tracking for Stolen Bikes

OK, It's for dogs really, but it should be possible to take this dog collar, re-factor it so that it can be powered by a self-sufficient power source and fix it to a bike... perhaps power it from the BB and put it in the downtube?

http://women.timesonline.co.uk/tol/life_and_style/women/the_way_we_live/article3501141.ece

The lockable collar, on sale from July, is made of anticut material to deter thieves and sends texts to the owner’s mobile telephone if the dog crosses a preset boundary. The owner can log on to a website where, using the sat-nav technology of the collar, they can pinpoint the pet’s location.

The collar is not cheap at £200, but its makers, Retrieva, insist that it is worth it.

I actually think £200 is worth it. I'd rather recover a stolen bike than go through the process of acquiring a new one. Plus it would get a bike thief caught.

I do want something like this, and in the past have considered just hacking an old pay as you go phone and seeing if the Ericsson developer tools allow you to send txt messages upon receipt of a txt (i.e. you txt it when it's stolen and it tells you the grid reference that it's at).