Since the rumors of such a project began, the name Google Babel has been attached to it. But now, some information posted by The Verge reveals that Google's unified messaging service will be called Hangout. The icon will be the same as the Google Messenger design except it will be colored green. Hangout will use the Holo UI and a swipe to the right will allow you to see conversations.
Until we hear the official word from Google, this is all speculation. Video chat feature Google+ Hangout already uses the name and it wouldn't be like Google to confuse users by using the same title twice. On the other hand, if Google+ Hangout is part of this whole unified messaging service, it might make sense.
Google I/O is just around the corner, so it might not be too long before we know for sure.
source: TheVerge via AndroidAuthority