Personally, I think that you should be committed if you buy a 2G iPhone three weeks before the 3G version comes out – no matter the price – but hey, that's me.
When Apple last offered refurb iPhones they sold out in two hours, so if you like flushing your money down the toilet, you'd better act fast.
AT&T requires a new 2-year plan, ordered during activation process. Limit one per customer.