I just wanted to add that if you use any app besides the official Google Voice app, such as GV Dialer, you'll have to add your Google Voice number to your F&F if you want to get free outgoing calls. GV Dialer will call your google number first, then run the script to make an outgoing call...like when you call your own number, press 2, dial number, press #.
If you don't have Friends & Family, then don't worry about it.
Oh, one more thing...if you give out your Google number out and someone has Verizon and he/she calls you, it will be free for you if their Caller ID shows up on your phone (since we have free IN calling). It'll cost them minutes during the weekday, but not you.