Not that anyone is reading this thread still, but just in case some of you are:
If you are missing incoming texts, calls, and/or voicemails, when you're in a covered area, this MAY NOT BE A NETWORK PROBLEM.
I had a Blackberry that had all these problems two years ago, and I eventually mentioned it to a savvy AT&T rep. He got me a replacement SIM card and all the problems went away as if by magic.
Also, just another anecdotal experience: I live in San Francisco and spend most of my time here, and I haven't had a dropped call since I got my iPhone a few months ago. However, I have run into numerous situations where the data connection stopped working. In fact, to give an idea of the magnitude of the problem: I walk to work. I like to listen to a streaming internet radio station, one which tacks a ten second ad to the beginning every time you start the stream but otherwise does not have any ads. The last time I tried to listen to it while walking home from work, I literally heard the ad for more total time than I heard the station. Which is to say, the stream very rarely worked for more than twenty seconds at a time.
-fred