Voxorin I’m not sure if this will be useful to many people, as it is a special case. I am successfully using the the nRF9160 Feather on FirstNet. This did require me to report the Modem info and IMEI to our FirstNet rep.
Voxorin I just realized I didn’t give you all of the information to put in the cellular provider matrix; Here’s a screenshot of the NRF Connect LTE Link Monitor with the device connected.