Originally Posted by PaulG1488
You shouldn't have an issue using another carrier. I've had friends who ran into this with other devices and just unlocked the phone and used it on another carrier.
I'm not sure if the other carriers do as well, however I am 100% sure that T-mobile and AT&T share their blacklists. So it will be useless to switch between these two carriers. How do I know this? The exact same thing happened to me. I bought an AT&T m8 and used it on T-mobile for a couple of weeks and then it got blacklisted after the original owner reneged on his contract and didn't pay the early termination fine. So phones also get blacklisted if contracts are broken and fees are due, not just if they are reported stolen.
The only legit solution that I can offer the op is to sell your blacklisted phone on ebay and CLEARLY state that it is blacklisted and for parts or export only. They work fine overseas and there is a market for blacklisted phones on ebay. So you should be able to recoup some or all of your money. Good luck