I don't know if Verizon would fit the bill, but the keyword to look for is "voip provider" (or "voip service provider"). As for protocols, I would start there i

I don't know if Verizon would fit the bill, but the keyword to look for is "voip provider" (or "voip service provider"). As for protocols, I would start there if I were you: https://en.wikipedia.org/wiki/Voice_over_IP#Protocols https://en.wikipedia.org/wiki/Voice_over_IP#Protocols