So, after spending a while on chat with Apple support today, it appears there are more details to Apple SIM that, at least I and my support agent, were not aware of. Specifically, everyone knows (or should) that if you select AT&T with Apple SIM you effectively become locked to them and unable to switch carriers. But, now it also seems that if you select one of the other carriers (Sprint or T-Mobile) you get locked OUT of AT&T. AT&T will no longer be an option once you've chosen another carrier. I learned first hand and while chatting with Apple support, my agent too discovered this after talking with AT&T himself. So, lesson learned..... Anyone with a same or different experience?