Wonder if any of you have used an unlocking service to get the 521 to work on a different carrier. For example, a search led me to this site: Get Nokia Lumia Unlock Code - Unlock Nokia Lumia Network. They promise an "unlock code" for $40.
You could always get service for 60 days from T-Mobile, then have T-Mobile unlock your phone, has long has you had service with them for 60 days and phone is paid in full. See this