Sometimes I'll call Bee's mom when I'm walking with the kids, and put her grandson on the phone so they can catch up. He's not that great on the phone though, and mostly just gives one word answers to her questions. After a while, I kind of gave up and just record videos for her so she can hear him talking.
Skype and Facetime have also been hit or miss, but after a brief warmup period, the kids sometimes get into the call. The problem with video chat is that my in-laws can't always figure out the technology on their side.
Are your kids good on the phone? What about Facetime/Skype?