You're thinking of purchasing a phone number through NumberBarn to keep your business and personal calls separate. But with call forwarding, how separate can they really be? Won't all your calls just show up on your cell phone bill anyway?
If you forward your incoming calls to an outside number, those calls may still show up on the bill you receive from that number's carrier. Depending on your incoming caller ID settings, they may appear as calls from your NumberBarn number or calls from the caller's number.
If you want to make sure none of your business calls show up on your personal phone bill, you can always set your incoming calls to forward directly to your voicemail. Then, return your customers' calls by placing outbound calls to them.