Google voice is the free way to set up a business phone number, however, I ran into a problem doing this for a business I started. I have two other partners in that business, so I wanted all three of our phones to ring when someone calls the business number. This is technically easy to do with Google Voice, however, all three of us already had Google Voice numbers, so we had to "disconnect" from our previous GV numbers to attach to this new one. Now, for us, this worked out, because none of us used our Google Voice numbers much. But, for people that already use it regularly, this could be a problem.
ChooseWhat writer, Kate Harrington just posted an in depth article on using Google Voice for a business line: http://www.choosewhat.com/starticles/using-google-voice-for-your-business-number
