I have Verizon and went from a decent Samsung flip phone to the G4. An area near my house in S.F. was always dead for the Samsung, but the G4 never drops a call. Inside my house, it could be better though.
The real surprise was in remote areas. We have a cabin in the Stanislaus National Forest, 17 miles from town. I was very curious to see how well the G4 did in such a remote area. Not only did I get service 200 yards closer to the cabin than with the Samsung, I was actually able to pull in the 3G network. Can't tell you what speed because I didn't really test it, but the Samsung couldn't get VoiceMail until I get all the way to town because it couldn't access the basic network well enough. I was very impressed with the G4's radio (again, on Verizon), but comparing it to a Samsung flip, I didn't think it would do as well for regular voice calls, let alone pull in the G3 network as well.