More likely, there's something wrong with that tower, and they just don't know it. (Or can't isolate which tower it is.) If you contact the provider, and can give them the tower ID and let them know what the issue is (no data, 2G/3G/4G, etc), good chance they'll fix it within a few days.
The N900 lacks the SIM toolkit needed to change that. But most service shops should be able to put the correct settings in the SIM to avoid that tower if you know the tower ID.