[HELP] LS980 with Cyanogenmod 12.1 on AT&T

Hey guys,

I have a decent little LS980 here that I put Cyanogenmod 12.1 on via TWRP. I would like to use this phone on the AT&T network but I cant seem to figure out how to do it so I thought I would ask you. I spent some time googling and researching but I am not having much luck. Any help or advise you can offer would be awesome!

LS980 no data on AOSP Ringplus nor Ting

Title says it all.

I've tried multiple AOSP roms. I've flashed hybrid bootstacks for ls980. All had no cell data. Calls work fine. Haven't checked texts as I use Google Voice.

I've treid a couple apn-conf.xml swaps, including swapping from stock 5.0.2 with working cell data, all to no avail.

What gives? It can't be impossible to run AOSP on non Sprint?