These phones support Cricket or other GSM networks?
Cricket is owned by AT&T but since the sale is for phones locked to the AT&T network, I would not count on it.
I have had AT&T iPhones that were not on contract anymore (past the two year contract). I would call AT&T and ask for an unlock code. I needed the phone’s IMEI and serial number (from settings) and then when I did an update on iTunes, I would get the message that the phone was unlocked. But since this deal states explicitly that the phone are AT&T only, you may have a problem getting AT&T to approve an unlock request.
I can only guarantee that this will work with AT&T