Read this article about Google Voice. I just received my Google Voice Tel.# and this has some really cool options. For one all calls made from this number in the US are FREE and I can call Germany at $0.02/minute which is a whole lot cheaper than what Verizon is charging me.
I can manage this number from a google.com website and initiate calls from this site. I type in the number I want to call and it calls both that number as well as dialing my number I specify to connect both parties up.