BGR has a report on the arrival of FaceTime video calling to the iPad and iPod touch devices.
“It’s actually pretty simple… Your Apple ID will be registered with your device/s, and that will allow other Apple devices to start a FaceTime call using your email address. Apple will also reportedly make use of push notifications to deliver these incoming FaceTime connection requests as we have been informed there is a push notification detector tied into the FaceTime frameworks in the new iPhone OS 4.1 beta.”
Source: BGR