Well I don't live in the US but it took me just a couple of weeks of being there with my N900 to realize that AT&T is total crap.

Sorry, dear pals from the US, but unfortunately once this actually happens you have 4 options:
1) Replace your phone and lose everything that only the N900 has to offer.
2) Switch to a local mobile provider if you're lucky enough to have one operating in your area on the N900-compatible frequencies - and get f***ed if you ever need to travel outside your local area.
3) Stay with AT&T and have only 2.5G services, as well as their total crap customer services.
4) Emigrate.