dear H.,
A friend of mine uses a web cam to stay connected with her daughter's far-away grandparents.
We have great grandparents and other relatives who are far away, and I keep lots of photos around for my son to look at, and I help him make cards and letters to send. He is only 2 but he enjoys making a picture or putting stickers on paper for his great great grandma and putting the stamp and address label on the envelope. Our relatives send him cards and letters frequently, over email and snail mail. (E-cards are very fun to send and receive). We also do phone calls. Whenever any of the relatives are in town, we make a point of spending as much time as possible with them. Same for when we are in their area, which is rare because of finances.
Another thing that I've found is helpful, since our in-town grandparents are usually very busy and not available, is we "adopted" a grandma. We found ours through my mother. Nana Storm was a volunteer at my mom's work. She had no grandchildren and so we met and hit it off and when my son was born, she became his surrogate grandma. He is actually closer to her than to his "real" grandparents, since he spends more time with Nana than anyone else (other than me!).
I am perfectly ok with him being closer to Nana than to my parents. He thinks of Nana as "his" grandma, and so she is just as much his grandma as my mother is. I guess what I'm saying is, try to maintain ties and build bonds between your child and his grandparents, but also, substitute your own extra "grandparents" or special adults to be in your child's life. While blood relations are important, I believe what is really important is the close bond between the child and the adult, whether they are related by blood or not. Sometimes you CAN choose your relatives!
If you don't know of anyone that you are drawn to to become a substitute grandparent, you can always check with your local Little Brothers Friends of the Elderly organization or other similar organization.
I am not trying to say blow off your actual relatives, just that sometimes it's ok to foster a relationship outside of blood family, so your child has someone who is reliably there for them who they can become close to. "Adopting" Nana Storm was the best thing I have ever done for my son, and I do not for one second regret it.