@cardiff-blues

I don't think I've seen a case of an N900 being sim-locked. The best thing you can do is just get a sim card and pop it in.

I guess Vodafone lost exclusivity.

Ok, I think you may have gotten through third party and not T-Mobile itself. If that is the case, it is extremely likely to be unlocked. I couldn't find evidence to suggest that T-Mobile even stocked the N900.