So it seems someone has finally gotten around to setting up a Dodgeball-like service for the UK. It be called BuddyPing.

Basically it allows you to register your location and, depending on your settings, notify and be notified when you're within a certain distance of your friends. Quite cool if you happen to be in the next pub down. Figured I'd have a play with it, so I've registered. Let me know if you sign up and I'll stick yer on me list.

Edit: Although, damn, is their email being slow. I'll be registered eventually...
Did you find anywhere that it told you how much it cost to send the login/logout texts?
Not explicitly no, but it has been suggested in several places (by the chap who runs it) that it currently at normal text costs to sent, and free to receive texts.
buddyPing cost
Hello there, owner of buddyping here. I have made a few changes on the main page and also the FAQ about the cost. Should have made it clearer. It is currently free to use the system, with the exception of sending a text which is the cost of a normal text.

Justin @ BuddyPing has now updated the FAQ to include information about costs.

9. How much does it cost to use buddyPing?

For the foreseeable future buddyPing will be free. We are still in the testing stage at the moment, but as time goes on and new users come on board, we will need to charge for certain aspects. Needless to say, all users will be notified of any changes when they occur.