Same thing happened to me yesterday. I tried to place a call and couldn't. I finally did a soft reset and when the system came back up, I suddenly had missed calls, voice mails, and e-mails going back a couple of hours. I returned a call and the caller told me that my number had rung 10 times before rolling to VM. That's about 5 more than usual.
This is really scary; the screen and connectivity bars looked perfectly normal before the reboot.
I'll add that my memory was ok. I had done my "daily soft reset" just yesterday morning.