Hard to say, it's AGPS but that could mean a network is totally required, or it could just mean that the time to first locate is reduced by being on the network (which means it will work even if you have the radio turned off, just take a while to get the first locate).
I do remember reading somewhere that it will work even if not connected to a network, but I'm not positive.
Wow these plans suck:
This encourages me to buy a first gen iPhone and keep my existing plan.
I guess we'll see if fido's any different.