Okay, new 8830 Sprint user and dummy. Came from Treo where mute button on top would turn off ringing on incoming call. I assumed BB mute did same but only seems to enter standby mode. What am I missing, i.e. just what does it mute?

Try the up volume button on the side.

It may mute the outgoing voice or on speaker phone????

The volume will mute the ringer. The button on top will mute the outgoing voice on a call. I believe on speaker or not.