Now, making a voice call using Hangout is possible, just because of its integration with Google Voice. It will allow users to send voice chats and voice mails. If you are missing your loved one, then you can easily send a voice message via Hangout app from your Android device which costs nothing.
Android Police has informed about the Google Voice integration. There is no need to update the service, the integration will automatically show on your Android device through a pop-up window entitled, "Migrate Google Voice to Hangout." After migrating it with Hangout, receiving or sending voice messages and voicemails will become easy.
Its like the biggest search giant has made it available much early as number of bugs have found. IT may happen that Google will bring the Hangout update soon with removing all the bugs and errors. Not every user will take the benefit of this new service as the service will be functioning for few users because of its server side switch.
It seems like Google is testing the service by providing this to limited users. Google has also made an announcement for upgrading the Hangout to make internet based calls.