To confirm:
Even though the iDEN phones from Nextel (Sprint/Nextel) have sim cards, the two wireless technologies (GSM and iDEN) are not compatable.
Sprint is due to release a new BB phone soon, however, even though Sprint & Nextel are now a conglomerate, I do not believe that the two services are interconnected (Yet?)
I have an issue with Nextel at our company, in that some of our "construction" type use Nextel and they want newer BB devices with Push-to-talk on the Nextel network. Everyone but Nextel seems to be getting a new BB device.
Sorry, we are in sort of the same boat.