I managed to get Lineage OS (v14.1) on T-Mobiles SGH-T999, working with a Ting GSM Sim card. Initially the phone with Lineage OS wouldn't even recognize the sim card at all. once i installed the T-Mobile SGH-T999 Modem packages (googled "d2tmo modem") i found an XDA-developers forum that was dedicated to packaging the modem software for the phone. with it the sim card is detected. also the APN's for Ting are pre-installed and properly configured accoring to "https://help.ting.com/hc/en-us/articles/205428698-GSM-Android-APN-Settings"