My worst moments of homesickness come when I'm thinking about my niece (2) and nephew (4). I can chat on the phone to adult family as much as I want, but I miss watching those two grow up. And to hear my niece start to put together sentences and start to develop a real personality is both wonderful and sad, since I got to spend lots of time with her big brother at that age. I just keep reminding myself that my beloved aunt lived across the country, and we only saw her once a year, but we looked forward to her visits months ahead of time.
Regarding your technophobic sister, you could always get a U.S. phone number through Vonage, and she could call that for nothing. That has been a lifesaver for us, and it's a tiny fee, especially when it means hearing from friends and family more often!