I left my n900 into Nokia Repair a few weeks back because my sim wasnt being picked up and so lost any connection to the mobile network. Went to collect the handset and was given an E7 as a replacement.

After a few emails back and forth to Nokia Care UK I got a phone call to say they managed to source a replacement N900 and its due to arrive tomorrow

I think if you get an E7 as a replacement then it's worth a try contacting Nokai again to see if they can get an N900 rather than just accepting the E7