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.
Check them out.
You can, but you will need a VOIP application for that.
Something like Skype works well over WiFi, since you can actually call phones (landlines or Cellular).
The Skype app is free, however calling phones is charged (but much less than AT&T was)
As you know the only limitation is you have to be in a WiFi signal range.