This offer is for those with a Kindle with Special Offers only. Turn on your wireless, click Menu, Sync & Check for New Items, then on View Special Offers after the sync has completed. You should see this new offer:
Buy an Android smartphone from AmazonWireless & get a $25 Amazon.com Gift Card
Click on the offer, then click on the link on the offer page sign up and get an email with the promotion code. Sign-up for this offer expires on July 23.
You'll get an email (right away), a link to the Special offer page. You have until August 23 to complete your purchase and you'll receive your gift card by Sept 23. This offer is limited to one per customer (not per device).
The list of "phones" includes not only the HTC EVO 3D 4G Android Phone (which I'm tempted by only due to the 3D screen and camera -- otherwise, I really like the Epic 4G that I already have), but the Samsung Galaxy Tab, for those that want an Android tablet with a cell phone plan. Personally, though, I'm holding out to see what Amazon brings out this fall (rumors now are saying a 7" tablet in the next month or two and a 10" tablet by Christmas).