I'm amazed that in none of the reviews I've read is there any complaint about the horrible sound quality. I bought a pair of iPhone 4s for myself and my girlfriend and we returned them the next day. We each sounded to the other like we were in a cave. This is with full 3G signal strength on both ends.

It's surprising because the 3GS and 2G always sound great. Never any hint of this hollow, echoey sound.