I got the same exact letter.  Of course I was suspicious and didn't call, but Googled instead and found this blog.  
Dumb scammers.

I got the same letter.  It is a scam.  There is no such carrier as "US Airlines"; it is designed to make you think it is from US Airways so you let your guard down.  More info here:
http://www.wgal.com/8-on-your-side/us-airline ... r-scam/20622384
-- and here --
http://www.deceptology.com/2012/05/i-won-i-won-us-airlines-letter-scam.html

Received letter today from National Association of Travelers asking me to call 844-824-4461 (Must respond by July 10th, 2014). I am always suspicious of these award qualifications for travel anywhere in the continental U.S. from any major airport. Retail value up to $1,450.00. I did NOT call; there is no cross-reference number. Letter is 'signed' by Margaret Burns, Customer Relations Manager. Logos at bottom from "COMPAIR-Explore-Dream-Discover", "Sustainable Corporations of America" and "National Association of Travelers".