This is an interesting idea, but I have to decline for another MVP this time around.
I personally use HelloTalk on iOS for foreign language practice and its quite nice. There are quite a few interesting apps in this space.
I wouldn't be able to confidently expect to deliver an MVP for a voice chat app in a weekend, based on my own inexperience with that sort of work. However, I would probably advise against building, and instead using existing chatroulette clones (there are many) or open source video/audio chat software (http://voicechatapi.com/, for example)
In my view the major challenges here aren't software/tech, but distribution and a strategy to get traction.