Can I make a call from iPhone 5s via WiFi? I have an iPhone 5s that ATT will not unlock.  Can I make calls via WiFi if the SIM card is still in it but I have no cell carrier? Phone is at IOS 8.1.3.
There are 2 VoIP apps that are widely used here in Southeast Asia. 

http://www.viber.com/en/#iphone

https://itunes.apple.com/app/id414478124?mt=8&amp;ls=1

Check them out.