how much is the new iphone 3g going to cost me if i sign up for a at&t contract?

right now i have t-mobile and up until the last few months i was really happy with them but im most likely switching to at&t and getting the new iphone depending on the cost of the phone, no i heard its only going to cost 199.99 but if thats only if your a current at&t customer resigning your contract or a brand new customer signing up. i wanna now whats this thing is gonna cost me and what the monthly charges for the iphone are.
WOW AT&T PLANS SUCK RIGHT NOW I PAY 49.99 FOR 1000 ANYTIME + UNLIMITED NIGHTS AND WEEKENDS+ 1000 TEXT MESSAGES I THINK I MAY STICK WITH T-MOBILE