Try this test and it should help your hypothesis:

Take a AT&T 9000 and a AT&T 9700 that have both been previously activated, remove the SIM cards from both then wipe both of the devices. Connect them (via a WiFi network that has access to your BES or BB router if serparate). Then attempt to EA each device.

From my testing I'm almost positive this will work with the 9000 but not the 9700.