Living overseas I have to deal with this whenever I need to call family in the US. If you want to call using your cell then you absolutely need to talk with your carried or the international roaming bill will be an unwelcome surprise when you get home. If you can wait for a WiFi signal there's plenty of options.
If you're both using Facebook you can voice or video chat through the messenger.
I use SKYPE to call my parents. Skype to Skype is free or Skype to a toll free number is free, or you can add money to your account like a calling card to call.
Whats-app is still widely used outside of the US. I've been using it to call the reservation desk to make payments and verify my information. As long as both parties have it the calls are free.
There's also Face time if you're one of those Iphone people
Jim