This is an area being cheap won't save you any money if you're really serious about your business. If you want to look professional, check out Nextiva. I have a phone plan through them, $35/mo get 3 lines including a toll-free 1-800# with a menu, a personal #, and a fax #. Rings to the softphone they provide, or if I'm afk it rings to iPhone. Best part though is support... I've had to call them 10+ times and they're always available. I'm not affiliated with them other than as customer, but check them out.
Just avoid using Google Voice of Skype,etc., nobody will take you serious when it comes up you're on a skype number (they will find out easily). There are other services too, look around you'll find some real providers. Just avoid the junk, you get what you pay for. Call somebody up to do a 100k deal on a Skype # and you'll see what I mean.
