I'm not sure if this will help as I'm not an Apple user, but it might pay to plug your phone into itunes and see if there is a carrier bundle update available.
I have seen a similar issue on a 3GS running on Telecom which (in messaging) would show only contact numbers but not names. A carrier bundle update fixed this.
I'm not sure if this is the case with your problem, but the symptoms seem similar so it might pay to check.
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