My post was very responsive. If you are waiting for someone to report the same scenario you are posing, you may never get the answer you WANT. There are just not that many people who do what you are proposing. I doubt anyone can tell yo how AT&T will react.
The refresh cycles for Apple products are fairly predictable. iPhones are updated at this point yearly in the summer. The "chatter about the expected new offerings this year (verizon, new features on an at&t iphone, etc.)" began the day after the 3GS was released on June 19, 2009. You impulse bought and didn't do your homework. Will I crave the next iPhone incarnation in June...probably. Will I be "locked into" my 3GS until 2011, yes, unless I sell the 3GS and shell out for the new phone. Do I have buyers remorse, no (assuming I weighed all pros and cons of a purchase and made the best decision I could at the time).