looking like this is a big issue with smart mode turned on . I found this fix on a droid x board but it looks like a default reset is needed if this fix doesn't work for you.
Hey, I have a solution that doesn't require a factory reset! And in fact, it's a lot easier than it may sound.
With the phone in the bad state, non-ringing state
1. Get into another voice call. Call yourself from another phone if you need to, but you can do it on your next incoming call, too.
2. Answer the phone.
3. Trigger the proximity sensor by putting the X to your ear during in the call, or by covering the top right corner of the face of the phone with your hand. The phone face should go black. Once it has turned black, that's enough. It doesn't have to stay blacked out any longer.
4. Now, put the X on its back so that the TOP of the phone is level - the screen is level. That means you can't use the table and just lay the phone down, because the camera hump will keep the phone from being level on the front.
5. When you hit that "flat front" sweet spot, you will feel a short vibrator pulse. This means the ringer is back on. You can now end the call (from either side of the call).
Getting the phone level so you feel the vibration is actually pretty easy -- the phone is fairly forgiving. This is so easy that I'm tempted to actually use the Smart Profile feature. Especially since mine is not going into "no-ring" mode every time. For some reason it's working correctly more often than not.
Much easier than a factory reset. (But we're still going to fix it.)
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