A great read is Kevin Mitnick's book, "The Art of Deception: Controlling the Human Element of Security". He talks about how he was easily able to get people's personal information from the companies they worked for.
At Amazon...
The cheapest most reliable system I've used is Faxaway (http://www.faxaway.com/index.shtml).
It's $1/month and $0.11 per page to the US. Other rates are here.
If you don't want to install any software or pay any money, Yahoo actually works pretty good. You can share contacts and calendars. It's basic functionality, but has more than you think.