This tip is for fellow Android phone users who, like me, are constantly muting calls and ending calls because the phone was pressed against your face. There is an app for that: Screen Suite
If you install Screen Suite from the Android Market, the app will (using default settings) require a slide to unlock the phone when on a call.
No more random-awkward-silenced-conversations! And if your friend has a Droid, Evo, G2, etc., please pass this tip along. :)