My biggest use case for ChatGPT voice mode is when I _need_ or _want_ to be handsfree. Think working around the house/yard, Driving, Walking around the grocery store, cooking, etc. I find that I end up using my iPhone's voice-to-text then simply communicate with text mode (in the case of driving, I stop). After all, once I have to touch my phone, it's just faster to work in text mode.
All of my devices know how to make calls. All of my devices know how to make calls from a voice command. All of my devices know how to hang up a call. This is really nice.