I find owning a Canadian iPhone in the US to be a great proposition. I never worry about "on-air updates" one day bricking my phone. I have no mobile contract. I can also resell my phone and expect to recover a lot of the value.
Combined with a Google Voice account it's just awesome!
I'm currently on T-Mobile pay monthly and have EDGE, which is enough to use with Google Maps. When I need faster service, there's often WiFi, or I can fire up my Clear mobile WiFi hotspot, which also doubles as my home internet.
Combined with a Google Voice account it's just awesome!