Dont think so, just wireless, 3g or wap.
If someone finds it and turns it off then no, I dont think its possible to find it just from the phones GPS
Is it possible to prevent the phone from being powered off when locked? I've always though this "find my phone" stuff was worthless as anyone stealing your phone will turn it off pretty quick. If it can't be turned off without a passcode, and the SIM is relatively fidilly to remove, then it may actually be worthwhile.