I just found out yesterday from AT&T that my IPhone 6 has free wifi calling and texting. I had to set it up because I have spotty cell reception in my house here in TX. But it means that when I travel to Europe next month I can make free calls to the US as long as I'm connected to wifi. This works for all countries except China, Saudi Arabia, India, Turkey, Israel, United Arab Emirates, Vietnam, Pakistan, Cuba, Iran, North Korea, Sudan, and Syria. It also includes free texting. Basically it means that if your IPhone 6 (or higher) phone is connected to wifi and you have this feature set up, the phone thinks it's in the US regardless of where you are. That means any calls or texts you make from Europe (for example) are counted as if you were in the US. This only works if you are on wifi, so if you left a wifi hotspot and your phone connected to a cell tower in Europe, you would be charged for international rate for calling/texting.
I had no idea my phone had this feature, so I thought I would share it with everybody!!