We both have Droid X2's, and frequently when we call each other at times we planned in advance, our calls go straight to voicemail.
My friend & I set our alarms for the same time and whoever wakes up first calls the other. But we both tend to hit the snooze buttons. Very early this morning my phone went straight to voice mail the first three times she called. A minute later, I'd shut off my alarm and it rang correctly. We're finally recognizing a pattern, and since the alarms don't consistently ring at the full volume expected, it's been causing us to miss some deadlines.