You said you bought 8 on launch day, that means you did not buy them "online".
With an online order, the buyer must activate the iPhone first to prevent fraud.
Since an Apple store employee physically handed the 8 iPhone's to you in person, there can't be any fraudulence claim.
For online orders, changing a SIM can't bypass the verification process, otherwise, any lost iP5 in the mail could just be sold by the thieve by swapping the SIM card.
Also AT&T use the activation process to track which iPhone has purchased/upped the contract.
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You said you received it today. So that means it is an online order.
I would activate it, tell the buyer it has been open for activation only.
Then ship the phone without the original SIM.
If you want to be a nice seller, include a brand new unactivated AT&T SIM for any US buyer, so the buyer can use it immediately.
I bought a total of 12.... 5 online and 8 in store the 8 online were from AT&T online... None of them had that screen