What is the cheapest iPhone plan and how much?

(Also, how much is the iPhone 4G) I've been wanting an iPhone, but can't afford one just yet… I need to know how much the cheapest service plan a month is and who carries it… I might get one for my birthday but it'll be a while… Oh well please help!

Virgin Mobile iphone is $30.00 a month, but the bad side of it is that you gotta pay full price.
I would also say sprint Iphone plans aren't that bad eather. Don't got with a at&t iphone since there always changing the plans and making you pay more money.