So wait... If I wanna buy the phone without extending my contract I have to wait MONTHS? WTF apple.. Screwing it's best supporters over again.
No, you will be able to. Some people here do not know how to word their posts correctly. Since you are saying you HAVE a contract, you will be able to buy an iPhone 4, at full price (most likely). I got the iPhone 3G the day it came out on contract. When the 3GS was launched I was no eligible for an upgrade, however, through AT&T pre-orders, I paid full-price and received the iPhone 3GS on launch day, June 19th, I believe? So, you will be able to get the iPhone 4 without extending your contract- because you already have a contract. AT&T isn't going to say "Oh, you've been with us for this long, but no upgrade? Well, screw you, no phone". If you want to give them more money for a phone, they will sell it to you.
However, for the OP, I do not believe you will be able to get an iPhone. As I said to SimGar- (s)he will be able to get an iPhone at full price due to there being an existing contract. You however have no contract, and I know that a friend of mine went to AT&T for the 3GS pre-order last summer and they said he needed to have a contract to get the 3GS. He did not want to sign a contract (wanted to sell the phone for much more than it's worth), and they denied him. So I highly doubt you would be able to buy the iPhone full price.
Bottom line. If you have a contract you will be able to get the new iPhone, whether you are eligible for an upgrade or want to pay full price or that one-year early upgrade price. If you don't have a contract, I believe, from past experience, you are S.O.L.