Hope I dont get screwed on the "while supplies last" part

EDIT: Ok I jumped in, the 280$ coupon (n900280) thing is input after u sign up for the flip-swap (trade in site) thing and choose what phones your sending in the coupon worked and it bumped up my trade in value by 280$. It just tells me to send my "Proof of Purchase" which according to nokia is the shipping confirmation.

I guess when I'll recieve my N900 i'll send my E61i with the proof of purchase and get some money back (hope it works)