Hey Great question. We use Skype services. It allows you to purchase a local number (in Florida for example.) Then using the Skype app on your iPhone you can call out. (saving your iPhone cell plan.) People accepting your calls will see the business number rather than your iPhones own number. ...
If I was you I would contact the guys from Altschool that just started one, and can probably help you with it. Contact on Twitter @rubenharris he can probably help you.