Since the advent of and widespread availability of the internet it has become simpler to communicate inexpensively with anyone in any part of the world. That is a real blessing for travelers and expats living abroad. It has not always been that way and no one appreciates this modern technology more than I do. My seven main ways of keeping in touch with family and friends at home while traveling abroad are listed for you below.

1. Cards and letters. This is the only method I presently use that does not in some way depend on the internet. I still find that friends and relatives get a kick out of receiving a picture postcard from overseas. The underdeveloped nature of the postal system or even the lack of one in some countries limits this method.
2. Email. Ten years ago having email was less common. Today it is rare to find anyone without email. Almost everyone today not only has email but checks it at least once a day. If your message does not require an immediate response, email is a good means of communication.
3. Internet VOIP Services. VOIP or Voice Over Internet Protocol is most commonly known as internet telephone service. I know of at least a dozen providers. My favorites in the last few years have been MagicJack and Vonage. Both provide a "back home" telephone number which allows you to make internet calls to family members as if the calls were local calls. Skype in some cases is cheaper, but only when making calls to other Skype members.
4. AIM, Yahoo, & MSN Online Instant Messaging. Each of these can be used when your established friends and relatives are online. The messages are instantaneous but has the limitation of only having the capability of messaging while both parties are online. These message systems are particularly appealing to the youth of today, and many adults are being converted to their use.
5. Facebook & Other Social Network Sites. You can also instant message with Facebook and some people do. But Facebook's advantage over Yahoo & similar sites is that you can leave comments or messages that can be responded to at a later time. Posting regularly on Facebook can give your friends a running account of your activities at any frequency you desire.
6. Online Diaries Or Blogs. The terms are not mutually exclusive. Any blog can be used as an online diary. There are however specific online diary services designed specifically for the traveler. By simply giving your friends the URLS of these diaries or blogs, they can keep up with your activities.
7. Family Websites. The free Google Apps, for example is designed for families or organizations and provides a customized gmail account specific to your domain name. However, unless you get the paid premier edition (still a bargain at $50/year), you are limited to only 50 user accounts. I have one, but have to admit that I have only used it very infrequently.