I have a phone-upgrade-eligible AT&T account. I want to purchase an iPhone 4S 32GB at the subsidized price ($299), and resell that unit, preferably sealed and unopened, on eBay. I expect to be able to sell it for somewhere between $550 and $650 based on completed eBay listings for such units. Then I'm also going to purchase a factory unlocked iPhone 4S 32GB ($749) to actually use. In this way I hope to end up with an unlocked unit for less than $749 net ($299 + $749 - $550 = ~$500). What I'm unclear on is how to handle the SIM cards and activation. Will the micro SIM in the unit I buy subsidized be somehow linked to my account even before I activate it? I have an existing AT&T SIM that I can cut to micro size (I have a cutter) for use in the unlocked unit. Is there any reason to get a new micro SIM from AT&T instead of using that card? Will AT&T automatically switch me to the iPhone plan even though I won't activate the subsidized 4S? In other words, when does the iPhone data plan get added -- when I purchase or when I activate? (I'm not interested in skirting the requirement for an iPhone-specific data plan.) Thanks for any help!