This is technique can be done using anyone's active BB sim card. You're only using the sim card initially to set up the BBM service books and enabling the Storm2 to send and receive PIN messages. Once you remove the sim card it's running on WIFI meaning no additional charges (or association) to that sim card.
This means that if I have 1 active BB sim card and three Storm2 BBs I can have 4 (1 real one, 3 spoofed ones) and all be chatting using unique PINs without incurring any extra cost. The only stipulation is that the 3 'fake' account would only be able to run on WIFI so they're not always 'on' if you carry it around. However if you're always in a place with WIFI, it's almost just as good as a real BB!
Rogers 7280 -> 7100r -> 8310 -> 9000 -> 9800 -> 9900