So I switched from 8 great years with T-Mobile to get an iPhone. Got the 3GS. With full bars, when 3G is on, the sound quality is sub-par. Even when the phone is dialing the number, the sound of the ring cuts in and out like I'm calling from the moon. When you're talking to someone- on my end, words are cut off and parts of some conversations are hard to understand. And here's the hitch...turn 3G off, make another call to the same number from the same location and sound is clear as a bell! Even the "ringing" part is clearer. It's a totally different sound quality with 3G off. There's no question about it. I've been through 3 phones, 3 trips to Apple geniuses, two calls to Apple customer support, and one visit to the AT&T store. No one in customer service seems to know anything about this issue- even though I've seen it on other blogs. I've restored, reset, retried, redone, you name it. I've even swapped out the SIM. The guy at AT&T let me try his phone and his was doing the same thing- but to him that's apparently normal. Seems odd that a 3G phone would have poor sound quality with 3G engaged, but sound perfect with it off. Does anyone else have this issue?