Had a mailer in with my Amex Corporate card:
"Fly US Airways anwhere in the United States, pay with the American Express Corporate Card, and you will earn triple USAirways Dividend Miles on each ticket purchased for $375 or more. Call 1-800-872-4738 and use code 2248 to register. You can book tickets on this promo on their website, travel agent, or their 1-800 #, Fine print on the back: Travel must be between 9/1/2000 and 12/31/2000, limit to triple miles on three tickets. Must register prior to departure. Not combinable with other offers, certificates, promotional offerings, or travel voucher. USAir, USAir Express, USAirways Shuttle, or Metrojet only."

1. What website? US? AMEX?
2. How do you register via the phone if you have letters in your frequent flyer number?
3. What is the website used for registration?

they mean book on the usairways.com website.

as to USAir Ft with letter in it, I assume you use the number on the keypad that the letter appears on.