Imwoblin,
You have my story. I too have been with AT&T Wireless since 1997. I bought gen 1 on launch day and 3g on launch weekend, and I am being told March 2010.
I called AT&T to find out, and I was told 18 month wait, but told them that March is 20 months after purchase. I was then told that 18 months was in error, that it is 20 months.
If I have to wait until March, I will wait for the iPhone 3G-SD (Super Duper iPhone). WWDC is only 364 days away. So Apple and AT&T will have lost a sale. I will be out of contract, and available to go elsewhere.
So to sum up: been with AT&T for 12 years, purchased both iphones opening weekends, gladly sign a new 2-year contract, but now being forced to wait for a new iPhone until a few months before my contract is up. If I have to wait 8 months for an upgrade, I will wait the additional few months so that I can be free of AT&T.