Depends on the iPhone you are adding; v1 iPhone = $20 data plan; 3G = $30 data plan. Unlimited Family Text Plan = $29.99 (best value for your family plan). No such thing as a price break for multiple iPhones, except that you can share a bundled amount of minutes. I've got 3 3G iPhones and 1 Blackberry, so all four phones have the $30 data plan, plus we share 1400 minutes with 6,000+ rollover minutes. Hope this helps.