Yeah especially AT&T will not unlock the ESN to be used on another network if it's on a two year contract or a payment plan under their payment plans for upgrading, they used to offer reduced and free phones but anymore no free upgrades, HOWEVER if you want to change to a new carrier, some carriers will pay off your payment plan and let you keep your phone and they'll sell you a new one on a plan,
IE: we had three lines on att and were paying over $200.00 a month, actually it's closer to $230.00+ with taxes and fees and surcharges and all that BS, anyways all of our lines were off contract and we wanted to switch carriers so I requested all three esn unlocks so we could move, well two went through and the third won't unlock because it's on the payment plan for another $500.00 or so remaining, T-Mobile said they would move us and pay off the last $500.00 to $600.00 on my payment plan and I keep the phone which att will unlock for me after they pay it off and I get to keep it, then they switch all three lines to their network and I can keep my phone numbers if we want to, I already have a near new iPhone 6S Plus I've only had a few months and it will be free and clear and unlocked from att when it's paid for by T-Mobile, plus I get another new iPhone 6S Plus on the same type payment plan I already had with att, and all three lines are now with T-Mobile, the good part is after everything is said and done and billed monthly were only paying $166.00 at the most, but we get a $10.00 credit per line if we stay under 2 GB of data from our unlimited everything plan (which we never go over 1 that data usage) so that takes the bill to $136.00 and we get another $15.00 discount if we do the automatic bill payment so now our bill is only $121.00 monthly instead of over $200.00, with att were paying a lot on top of our package price with taxes and other fees, with T-Mobile the price of the plan is the exact price that we pay, all fees and taxes are included in their plan pricing, so $40.00 a line means $40.00 a line total so we're not ending up paying $40.00x3+ taxes and fees and surcharges and all that stuff which is what made our bill $230.00+ but now we're done with att and we don't have any contracts, I have three free and clear newer iPhones and one on a payment plan so I have a spare as a backup phone of one gets broke and we're paying less then half what we were with att so it's a win win WIN and I'm not paying off two phones and I'm not locked to any network so if I want to change again I can anytime, I also have a couple other newer cell phones from past att free upgrades when they still offered free or reduced price upgrades, so we're set real good, I think we have three spare unlocked cell phones now, two iPhones and a Samsung galaxy S5 that's waterproof to 3' feet underwater so it's good to change from att, you should try it too, soon!!!!