Jellybean, please try to accept the situation as it is and do your best with that. Let go of any guilt or resentment if you can, it won't solve anything. Imo, the idea of sending snail mail is great. I'm fortunate enough to live near my grands, but they still enjoy getting a card or note from me in the mail sometimes. Little ones love receiving mail, Iv always noticed.
As for skype, they will probably talk longer as they get older. I know you don't like seeing yourself, but isn't it worth getting to talk to your gc? I don't remember ever seeing myself on ft (haven't used it much though), so maybe that's a better solution? It's great that ds still keeps in touch even though you aren't close. Some ac wouldn't.
When the kids are older, maybe they'll be able to come for some long visits if that would work for you.
I agree with NandG that "you can build a good long distance relationship" with them. It will take time, but I'm sure you'll do it.