You can receive Google+ Hangouts invites and voice chats (from one computer to another) in Chat. Just download the Google voice and video chat plugin and sign in to Chat to get started.
Whenever someone calls you in chat, you’ll hear a sound notification and a chat window will appear. To answer a voice chat, click the Answer button in the chat window or click Join Hangout to accept your hangout invite. You can ignore the call by clicking the Ignore button.
If you miss your call, don't worry. The chat window will open with a message saying who attempted to call you.