A while back, I posted an entry on the possibility of FaceTime for Android in the form of Apple's new iPod Touch. Finally got to test and confirm it using Barnacle Wifi Tether and an iPhone 4. Signal is fairly stable although it's more dependent on your provider's 3G/EDGE network... GPRS is too slow to give decent performance and will most likely drop the call all together.
Barnacle's only shortcoming is the inconsistency of it's connection to the iPhone/iPod Touch. Hopefully those running 2.1 Androids don't experience dropped signal when the screen saver kicks in. So far, those on the Sony Ericsson X10 Mini/Mini Pro will need to run something in the background to keep Barnacle from switching to standby. Some users have reported firmware updates fix this, but not all regions have the same firmware. In this case, the screen saver/power saver is usually the culprit since it disables the wifi antenna to conserve power.
To make a FaceTime call, go to your contact list, tap on a contact and scroll all the way down and click on the FaceTime button on the bottom left.
A menu will pop up to show the possible ways to connect to the contact via FaceTime. A caveat, just because FaceTime will attempt to connect, doesn't mean that contact has FaceTime. You have to know which phone number or email that particular contact is using for FaceTime, and that contact has to already be online when the call is being made.
The iPod Touch has effectively given FaceTime to Android. Although those with a 2nd jailbroken iPhone and tethering should also be able to use FaceTime on their iPhone 4 while on the move.