Where can I set up a phone number for business that will forward to my cell phone?

Call forwarding is a paid for (unfortunately) service from most phone providers. You can either get a new number with voicemail (for when you want to turn forwarding off) and add the call forward feature to it. Or call your provider and have them add call forwarding to an existing number. It normally is a few bucks a month to have this feature added.

I am not aware of any software that can be added to a phone that would do this for free. Forwarding takes place at the phone companies main computer (switch) and they reroute the call from there not where your phone is located.