Customers are being notified through the Sprint Zone app, which leads to the mobile web page you see to the right. It's not clear whether or not this sale includes all EVO 3D accessories, or only some, but it's still a good deal.
It's also nice to see that Sprint isn't entirely forgetting about current EVO 3D customers who can't or don't want to upgrade to the EVO 4G LTE yet. Of course, a case could be made against Sprint's treatment of customers through the delay of the Ice Cream Sandwich update, but that's another issue entirely, so let's not go there.
Anyway, if you decide to take advantage of this offer, be sure to let us know what you get!