What does Clean ESN, ready for activation on swappa or ebay mean? - 1

I'm about to buy an iPhone that's new and also listed as Clean ESN, ready for activation. I know that means i can activate it with the carrier its locked to which is ATandamp;T but can i use online unlocking service like iunlockpro or any another one to unlock it so that i can use it with any GSM? Or is this only for the carrier its locked to since it new?

Clean ESN means that the CDMA phone, can be activated on any CDMA carrier, Sprint, Verizon, etc, a clean IMEI means that it can be activated on any GSM carrier, T-Mobile or AT&T, etc. Also that the phones have not been blacklisted by the carriers for non payment or past due bills.

So for a CDMA phone to be unlocked to work on a GSM network, that phone needs to have both CDMA and GSM radio hardware inside. So looking at the ad, does it state this? And if not does it state that all sales are final? The reason I ask is that you do not want to buy a phone that CAN'T be used on AT&T even if it's unlocked from the original carrier. SO make 100% certain that this particular phone can be used on AT&T.