Okay, this is obnoxious.
There is this awful little bug in iOS that I once thought was a Verizon problem. Then, I heard John Gruber mention it on The Talk Show a while back — and attributing it to AT&T.
Sometimes when the iPhone loses its 3G connection, it’s unable to get it back, and sits on 1X (or EDGE on GSM). The only fix is to enable then disable airplane mode.
Unacceptable, inconvenient, and messy.