It has nothing to do with ringing. The phone rings fine, it's the silent call bug. I answer the phone no sound and nobody can hear me. Hang up they call back same thing. Hang up I call them I never hear the rings etc. The only way to fix it, is to reboot the phone.
I have found through a bit of Googling that this has been reported across several forums, and apparently HTC and Verizon has admitted it's a known issue and they are working on a fix. This goes along with what Verizon told me last week when they told me Google/HTC where looking to push a patch out to the Eris/Incredible, and Moto Droid....not sure why the Droid. Anywho....it hasn't happened before and it hasn't happened the rest of today, so go figure.