I wish I had read this thread before buying my apple ultra 3. It worked for about a month, then suddenly a "No SIM" message. Same issues setting it up again - get the AT&T unlimited wearable plan, go through the motions for setting it up, then it goes back to the watch and says "Plan not in use", then I have to delete the plan and try again. Still, no joy. Of course with Apple's crappy return policy, I can't return it, I can't get it to work on AT&T and I'm stuck with a $850 phone with no cellular service. Corporations suck.