Google Voice is one of my favorite applications. I use this telephone service several times a day. It has transformed the method I use for phone calls.
With Google Voice, there is no hardware to purchase and no new telephone equipment required. You can use it with or without a computer. The voice calls are never sent to your computer so you don't have to wear headphones or anything like that. You simply use the normal telephone(s) you already have.
You can read my earlier article at http://blog.eogn.com/eastmans_online_genealogy/2010/06/google-voice-is-now-open-to-all-us-residents-and-is-free.html
Google had originally announced that all outgoing calls to US and Canadian telephone numbers would be free of charge until the end of this year. However, today Google announced the company is extending free calls through all of 2011.