Ok, I have the same problem as many other folks here. After many resets, I still have the same problem. Being an Engineer, I knew there must be something that was different in configuration from when my unit worked to when it stopped working. First, I replaced the battery with a new one. While this helped my battery life situation it didn't help the no ringing situation.

As far as the Sprint network changing, well it does... But that won't effect the performance of the phone except make it better.

The most effective setting that I found is:
Start-Settings->Phone->Options:
- Location (GPS) off
- Phone these settings don't matter
- Other settings don't matter
Start-Settings->Sounds and Notifcations
- Volume: Events are enabled, Programs disabled, other doesn't matter
- Notifications: Disable notifications on everything but Phone:Incoming Call
Start-Settings->Power
- Device Speed: High Speed

Joe