To use Google Talk video call you need to have PR1.2 update (30.2012.07-1) in your N9 device and download the Gtalk Video Call application from the Nokia Store. Once you have installed the application, the device will automatically reboot.
If not already activated, activate the Gtalk account in Accounts > Google > Google Talk.
Video calling is fully integrated to Contacts and Phone applications on the phone and there is no separate application icon for this feature. The persons to whom you are calling must have Google Talk Video Call capable device (mobile/tablet/computer).
To start a video call, open the Contacts application and select the online Gtalk contact to whom you would like to make video call. The contact card shows the Video Call button under the Gtalk service. Press it to start the video call.
Tips for using Gtalk: