So I hate to be the bearer of bad news but I think I have some answers.
First, the unlock screen you are talking about when the boots up, is it a lock emblem that shows one side slighty unlocked right when the phone starts? If so that does not mean the phone's radio is unlocked. It means the bootloader is unlocked to install custom roms.
After seeing this I was curious, turns out that US Cellular purchased the "regional CDMA" variant of the Moto X. Basicially its CDMA and LTE only, no GSM, so no TMobile or ATT.
Heres a link to PhoneScoop:
Motorola Moto X (regional CDMA) Specs, Features (Phone Scoop)
Hope this helps
Austin
Edit: Installing a custom ROM has nothing to do with the devices ability to communicate with different cellular networks, especially when missing hardware.