How does iPod Touch 4G FaceTime Work?

If you have an iPhone 4 and you want to FaceTime with someone you can call them and then click the FaceTime button. With an iPod Touch you cant call and you don't have a number to distinguish you from another iPod Touch owner. So, how does Apple go about this? They use email addresses. Namely Apple ID's. So, you can use the email you already have with the Apple ID or as Apple says "just enter your Apple ID and email address. Or create a new email account just for FaceTime. Using FaceTime is as easy as it gets. Say you want to start a video call with your best friend over Wi-Fi. Just tap the FaceTime app and find her entry to start the call. An invitation pops up on her iPod touch or iPhone 4 screen asking if she wants to join you. When she accepts, FaceTime begins. It’s all perfectly seamless. And it works in both portrait and landscape. See how much fun you can have."