I was originally reluctant to post this … simply because Cingular reps are not confirming this and claim no awareness of the offer so it seemed a little hokey. But given the site and the fact that many other companies use them for rebates, it MIGHT (use at your own risk) be legit.

Go to the site, give them your IMEI (no proof of purchase needed), phone number and address… that’s pretty much it.

I’ve done it so if I get my extended battery I’ll let everyone know. To my understanding if you recieved an extended battery in the box, you will NOT be eligible for this offer.

Link to original Cingular Forum post 

Link to Cingular® Rebates