Google Voice integration with Hangouts is just a matter of time. We wrote about it earlier this year. Hangouts would then be Google’s unified chat client, it would serve all your communication needs. This merger of sorts is one step closer to completion.
A Reddit user managed to get a screenshot of Google Voice integrated Hangouts app thanks to a debug menu. Mentioned user used an app called #DebugAllTheThings in order to get it to work. You can download the debug utility on the XDA page linked below and see it for yourself, though you’ll have to be rooted. The integration won’t work, of course. You can try to run it but you’d be out of luck, the best you can do is get what is shown already via the screenshot below.