iPhone 3Gs - compatible with AT&T

My iPhone died on me, the screen is almost too dark to see anything on it. <insert sad face>

I still have time left on my AT&T contract - I don't want to use my upgrade & renew for another 2 years.

Does anyone have an iPhone 3Gs they would like to sell me? Anyone that already upgraded to the iPhone 4 & it's just sitting around?

Thanks!