The Kindle Fire HD is, at the moment, the best Android tablet that's not really an Android tablet but is still kind of an Android tablet. The LTE model, while pricier than the others, is handy for those that still need to download on the go. Now, AT&T is going to start selling the connected model for $399.
As a temporary introductory offer, AT&T has a "deal" that allows customers to sign a 2-year contract in exchange for $150 off. Unless you know for absolutely certain that you'll need to use mobile data on that Kindle Fire HD every single month for the next two years, though, you might be better off just paying for your device.