Found this posted on another site. Looks like this could help for anyone with issues on these Samsung phones (USA, Exynos).
"I have confirmed these applications will allow you to use VoIP via your LTE connection as a bandaid till VoLTE is released. Both can be found in Aurora and are a “quick fix”. If someone is on T-Mobile the “DIGITS” app is included with their subscription already at no additional cost. With the magicApp you can buy the hardware for home VoIP & a 12 month subscription for the same price as just the app via G*#gle Play(for 12months) and not have to login to the Gapp store or give them a commission. My advice is to buy direct if going this route, not via GPlay store.
For non-FOSS apps having only 1 or 2 trackers was surprising to me. We know how to block these if they are “non-essential” obviously. The permissions… Another story but these apps are managing calls and SMS/MMS so a bit more understandable.
magicApp Calls/SMS only
Links for Aurora Store: