Is TLS good enough to secure VOIP calls?

I do consultations for clients (mainly SMBs) for VOIP solutions. I usually point them towards a reasonably-priced VOIP solution that covers all the essentials like Grasshopper or Talkroute.

One of my clients is based in a jurisdiction with very strict data protection laws. They also manage sensitive records for the local government, so they're super paranoid about call security.

I've been looking into various options here. As far as I can see most VOIP solutions encrypt calls using HTTPS, so presumably the call content is protected no matter what platform you choose?

I'm just curious to know about other people's experiences with this: as far as I can see SSL/TLS is good enough for call security. Do you guys agree this is sufficient?

I know it won't protect metadata like device IP addresses but surely TLS is good enough to keep calls private?