I use a blackberry bold on the very same AT&T network and haven't had any such problems in any of the metro areas where I've used it, including:
- San Jose / Silicon Valley
- San Francisco
- Los Angeles
- San Diego
- Portland
- Seattle
- Las Vegas
- Houston
- Dallas
- Oklahoma City
- Des Moines
- Minneapolis
- Chicago
- New Orleans
- Atlanta
- Charlotte
- D.C.
- New York
- Boston
Maybe it's not all the network....