I have great news for potential and existing Viber users. Calling a contact on Viber is absolutely a breeze. I called a friend from messages we have exchanged. Although the call didn't go through (after ten times the call will end), he did at least get a notification to say he had an incoming call. So he rung me back using the recents tab of Viber, which absolutely resembles the recents tab of the phone app, so no problem there! He opened Viber by double tapping on the above notification. Anyway, I then got an incoming call, but because Viber was in the app switcher, it was just a case of double tapping on the app then double tapping on the answer button. By the way, nice ring tone they have! Using headphones along with the phone's mike, the call went very smoothly. Quality was excellent. No breakups or drop outs, someting familiar with cellular calls, and I was even able to activate the speaker by double tapping on the speaker button! I was also able to end the call with a double tap of the end button. Not sure if two finger double tap works here to both answer and end a call. So as you can see, calling with Viber is very accessible and easy to do. But may I suggest you wear headphones as you could inadvertently activate the phone when using the earpiece. Also, may I suggest you either mute speech with a three finger double tap or turn VoiceOver off altogether with the triple click home method if you have that set. I found this out the hard way when VoiceOver blasted out a notification through my headphones. Lol! Anyway, hope this is useful. Enjoy!