Caller ID Help

Just recently my phone has started showing "unknown number" on my caller id when I miss calls. This does not happen all of the time, and at first I just thought that maybe someone from an unlisted number was calling, but it happens often now, plus, if the preson leaves a message, even if my missed call log says "unknown number", when I look at the voice mail information at the top it will tell me who the voice mail is from, so the phone recognizes the number to disply along with the voice mail, but not to display in the missed call log. How can I fix this?? It is driving me crazy.

Including your Address Book in Content Protection will prevent your Caller ID from using it to look up numbers during incoming calls. Check your Security Settings. Options / Security Options / General Settings / Content Protection Enabled
Include Address Book: If yes, change to no.