I think in terms of interaction, relationship building and efficient communication face to face communication is simply the best way to keep in touch with a person or even people (if it is a group event or you like to talk to lots of people!).
However, the situation may demand different resources. I have family and friends that live overseas, so the best way for me to stay connected is by the internet and more specifically Skype and Facebook. I also email them from time to time.
I also have family without access to these resources and in this case my best (and in actual fact only real viable ) method of staying connected to them is through my mother, who writes letters from time to time.