It seems rare that VOIP providers offer a secure tunnel using TLS. I have 2 providers and neither support TLS-- which is reckless because phone conversations are more sensitive than using the web. Conversations are not only quite personal but the realtime nature of a spoken conversation encourages people to divulge things faster than they can think about security.
It’s a shitty trend particularly when unwarranted surveillance in the US has targeted VOIP specifically. And why not… it’s in the clear.
Sure, there is the problem that TLS can only secure one segment of the conversation. So if you call your doctor or lawyer using a rare TLS-capable VOIP provider, it’s only secure to the VOIP server and thereafter it’s in the clear. Is that the rationale for VOIP providers not bothering?
Always remember that no business cares about us. It’s a natural law.