Voice is the most separate and distinct. I use my google voice number whenever I sell or buy anything on CL and I'm sure there are many other more creative uses.
I was really hoping to see some love for Voice on iOS 10 after they added the new messaging and voip features, but I doubt there is much hope of that actually happening. They have yet to release a version suitable for iPad, let alone integrating with new features.
I just use it to manage my voicemail, are there any viable alternatives?