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Android device users will be able to use video and voice chat with any Google Talk contact using another Android devices (phones or tablets) or Google Talk on Gmail. The features will work of standard 3G, 4G and Wi-Fi connections.
According to the Google Mobile
Using the new features is simple. On your Android device, from the Google Talk contacts list, you'll see a video and voice chat icon next to each contact. Touch the button for the feature you'd like to use, and chat away.
Video can be paused while audio chat continues if you need to navigate elsewhere during a video session. During voice or video chat, text chats from that contact are overlaid on the device screen.
Here's a brief demo of the new features: