A video telephone / video chat service somewhat similar to Skype and Google Hangouts that makes it possible to conduct one-on-one video calls between newer Apple iPhone, iPad, iPod touch and Mac notebooks and desktops.

FaceTime Requires AppleID

Apple's FaceTime service is free to use but does require an Apple ID and a Wi-Fi connection, although future versions of FaceTime may also work over 3G and/or 4G connections, and several apps are currently available that make FaceTime over a 3G connection possible on a jailbroken iPhone.

FaceTime first debuted in the second half of 2010 on the iPhone 4, and currently supports the iPhone 4 and later, iPad 2 and later, the fourth generation iPod touch and later, and Macs with Mac OS X Snow Leopard (v10.6.6) and later installed.  Some FaceTime features, like 720p resolution, are only available on certain platforms such as newer MacBook Pros and iMacs.

FaceTime Compatibility

FaceTime is incompatible with non-Apple devices as it is a proprietary app and service. For non-Apple users, there exists a number of alternative Android apps including Google Hangouts and Skype.

(webopedia.com)