Google has begun OTA distribution of Android 2.3.4, and as expected one of the features it enables is video calling in Gtalk. The video functionality - rumored earlier this week - is for Google's Nexus S, and functions not only over WiFi but 3G/4G connections, presuming your carrier allows it.
The OTA update will supposedly be hitting the Nexus S "in the next few weeks" and then arriving on other Android 2.3+ devices "in the future"; it will also bring bug-fixes for the original Nexus One. There are more details on Gtalk video calls in the help center.
Meanwhile, Google is promising another surprise for Nexus users, though right now it's not saying exactly what that might be. No word on if there's a manual way to trigger the Android 2.3.4 update, but we're guessing one will be winkled out very soon.