Still (11/11/2010) same problems on Chicago T-Mobile network (after having read the many comments here, with common thread being T-Mobile, I definitely exclude this as being a Nokia N900 problem). Three questions for those more up to date than I:

1. Is a SIM card swap confirmed as possibly restoring the service?

2. Could someone confirm that a new(er) SIM card has a set of numbers in the upper right corner (aside from those running "horizontally", as described to me by a T-Mobile rep, when troubleshooting other issues a few weeks ago)? Is it true that's indicative of 4G support in the card?

3. Is Nokia N900 capable of using 4G on T-Mobile USA?