During the day, got a new voicemail from a friend, but never got any notification of a missed call. Wrote it off as just having been inside a building, and maybe I didn't get a good signal or something with AT&T. During the day, was making calls and sending/receiving texts with no issues. Later in the day, same thing happened again, VM, but no missed call notice. This made me curious, so I started testing it again with my wife's phone, and same thing. Had to do a hard reset on the phone, and finally it started working again. Anyone else experiencing this? Could it be a SIM card issue? I previously had the NO SIM INSERTED issue a few weeks back, but never had that happen again. Any thoughts?