Using Whatsapp with internet calling international. Is it free?

My friend in Ireland told me she calls her brother in Miami for free using Whatsapp with internet. I know I can call the U.S. and Canada with my Telcel plan for free, but with cellular data off, can I call other foreign countries using Whatsapp with only internet connected for free?

I think the other party also needs to have WhatsApp and be connected with the Internet. Then it's a WhatsApp to WhatsApp call. Works just like Skype or Facetime, etc., etc.

Exactly....use Whatsapp to Whatsapp to Ireland from Mexico all the time.

I whatsapp Ireland too with a typed message but have never made a phone call through whatsapp.
when you say you whatsapp to whatsapp to Ireland from Mexico all the time, are you calling and talking or typing messages back and forth. There is a little phone picture on the top right of my whatsapp when I open it up and if you tap it, it will call the person you have chosen to contact. This is what I am am not sure about. If you tap the little phone picture, it will call the other whatsapp person, but not sure if it is free on wi fi.

It is free. Been using it for years. Works for both local calls and long distance. No time limit, no number of calls limit.

Cool.