I just received my ATIV S from Negri (took 2 days - no issues) and I have an AT&T Micro-SIM, however now I am stuck trying to activate it on AT&T. I had no problem before with other unlocked phones but AT&T claims the Ativ S (Samsung I8750) phone does not exist in their database so they cannot activate it on their network. I would appreciate anyone giving me an idea of how to proceed!