Why not support the device from Xiaomi, the 3rd largest global cellphone maker?
I had a Xiaomi 10T and it is technically compatible with ATT 4G network. It is proved that it can join your 4G network with both data and phone call with VoLTE. However, your system keep on restricting me from using it with my ATT account and I had to keep calling the customer service to lift the restriction. Excluding the devices from the 3rd largest global cellphone maker is really not customer friend.