it is on hangouts for years. and it suck in all and every way imaginable. if there was a way to make it suck, they did it.
you have to keep switching accounts (close conversation, press hamburger icon, click account icon) everytime! got a SMS? switch to the confusing SMS account. Got a SMS on your google voice account? switch to the account (gets better if you have two!).
Dial via google voice? had your SMS account selected last? you will only get a "can't dial" error and the app closes.
it is the worst wtf fest of all google screw-ups in usability ever.