Update on AT&T Closed Cell Phone Network

On a whim today, I put my AT&T SIM card in my old unlocked Blackberry, just to see if it could make and/or receive calls. This is the same phone that previously worked on the AT&T cellular phone network, then mysteriously became unable to operate as a phone around December 1. At the same time, two brand new unlocked Motorola V3 phones also refused to work with AT&T service. At first AT&T insisted that all three phones were defective, then later stated that they had shut their cellular phone service to unlocked phones. Perhaps they changed their minds? I guess this will remain a mystery.