The Hangouts for iOS app is cross-platform and not only does it allow people using different OS to communicate, it also allows people using a desktop system and a mobile system to talk. And if you are on a device powered by Google's open source OS, no need for jealousy. You will eventually be receiving the same update that the iOS users are now enjoying.
Besides allowing you to make those free calls to the U.S. and Canada, the update also adds animated GIF support and incoming calls now pause your music instead of turning it off. Yup, it's all good for iOS users and if you don't have Google Hangouts on your iPhone, iPad or iPod, now is the time to install it.
source: Hangouts (iOS), Google+ via Engadget