Sprint has spotty LTE coverage in the Dallas area. The coverage is very iffy in the Allen area. It's spotty between Allen and Love Field. It's very good at Love field. It's like the old Sprint days again when they had spotty phone coverage.
VerizonFios, Callcentric, Future-Nine, Vitelity, CallWithUs, Voip.ms, Anveo.
A stable system doesn't have enough features.