Phone doesn't ring or show missed call, later a voicemail appears I have an AT&amp;T Samsung Galaxy 2 and have had a sporadic problem:  A person calls me, my phone doesn't ring, kicks them over to voice mail, doesn't show as a missed call, and then the voice mail shows up on my phone as much as an hour later.  I have tested this from my land line and sometimes the phone does everything it's supposed to and other times doesn't ring and doesn't log a missed call but records a voice mail.
I had the same issue. You will have to change your phone notification settings. Go to "settings," then "call", then "phone settings" under "other call settings."  Scroll all the way to the bottom of the call setting screen and select "phone notification preview" (To show caller ID for missed calls and voicemails on locked screen and status bar).

Most likely, you downloaded an app on your phone that adjusted your phone settings. I hope this helps.