I realize this is an old thread, but I'm experiencing the exact same problem after upgrading my 2g iPhone to the 3.0 firmware. HELP PLEASE !!
1. The iPhone cannot receive incoming calls once it enters standby for over a minute or two
2. Once the phone enters standby, it will neither ring nor vibrate
3. If I press the home button after the incoming call has ended, there will be a missed call notification, stamped with the time I pressed the home button (not when the call came in). Also, once the phone emerges from standby, queued voicemails and texts roll in, often from hours prior.
4. If I press the home button while the incoming call is ringing (on the caller's side), the iPhone will ring and vibrate immediately, no problem
5. Before the phone enters standby, there is no problem receiving incoming calls - the iPhone rings and vibrates just fine
6. When the phone is being charged, there is no problem receiving incoming calls - the iPhone rings and vibrates just fine
I have disabled push (with google contacts/calendars), push notifications, "reset all settings," restored the iPhone using a backup, restored the iPhone "as a new phone."
Everything except a jailbreak to install the program "insomnia," described in the link, here:
http://themobileexperience.blogspot.com/2008/11/solution-to-iphone-wont-ring-problems.html
HELP, PLEASE !!
Thanks!