You can also try using an IMEI from one of their demo units. Thats what the store did for me on my 2nd T Mobile card for my 2nd P2. Apparently it doesn't matter if there are duplicate IEMI #'s in their system.
Absolutely... They just need to use a tablet that will validate in their system. After that you are good to go. The T-Mobile network never verifies anything again after that. You can use that SIM for the 200 FREE megabytes per month in any GSM device after that.