I'm a Nana and I'm the one who left my grandkids - though I'll be back in the U.S. every year for a couple of months. In the meantime I Skype with them. My youngest granddaughter just turned four and figured out how to Skype me so now she does - sometimes 4 or 5 times a day! I think I see the grandkids more now than when I lived 45 minutes from them. I put my laptop in the kitchen and talk with them while I'm cooking or doing other work. It is almost as good as being there - I just can't hug them.
In spite of my watching endless documentaries on youtube - plus daily Skype sessions (not just with the grandkids but with friends) I've only use 17 gb's and I'm more than halfway through the 30 day billing session.
Is your father computer-savvy? If not, I'd set him up with one and show him how to use Skype. It will help.