How much is it to add an iPhone line to a regular plan?

well first off it depends on what company you choose. either Verizon or at&t. with at&t you will probably, if you want unlimited, pay about 100 dollars for the one line excluding how much you pay for the actual iphone, they can range from 200 dollars to 600 dollars all depending on GB size, the highest is the 64gb. but if you don't want unlimited and want a flexible plan that works for you, you will probably be spending roughly 70 dollars a month.