How to unlock a Photon Q with an MSL code?

I'm having a strange issue with a Motorola Photon Q. The Photon Q is carrier locked to Sprint but has long since been paid off. I have the IMEI and the MSL code to unlock the device to use with other carriers, but I've hit a roadblock in actually getting it unlocked. I called Sprint and the guy that answered seemed very helpful. He tried to unlock the phone. He even read through the manual to try to make this work. In the end he talked to his supervisors and informed me that because of how old the Photon Q is they can't unlock it through IMEI and that I need to go to the carrier that the phone will be used with, AT&T, and have them unlock it using the MSL code. So, I went to AT&T to talk with them about unlocking it with the MSL code and they didn't even seem to know what an MSL code was. I explained to them exactly what the Sprint guy explained to me several times but they didn't seem to understand. They wanted the IMEI, which didn't work. They kept asking me if it was an AT&T phone. Nothing I said seemed to get through and I still don't know how to unlock this phone. So, how do I unlock this phone, the Motorola Photon Q, to be used with non-Sprint carriers like AT&T?