I didn’t know whether to laugh or cry when I first read about this, a cell phone for your pets, PetsCell™.
The PetsCell is a fully waterpoof voice enabled mobile phone that you attach to your dogs collar. Your dog then has it’s own number you can call it on, so if he gets lost you can call him up and ask him where he is, woof once for the park or twice for the nearest lampost.
For a more accurate location you could use the built in GPS which you can track online or via a 3G phone. Though this must raise privacy concerns for all 4 legged friends.