I agree with jumpgate that the best way to use your voucher is just call USAirways and tell them you are using a bump voucher.

And yes, be aware that for availability purposes, these vouchers essentially book as award travel, so on the most desirable routes, you may find that no seats are available, even many months in advance.

On other routes, you will have no trouble using your voucher. You really need to call to find out for sure. I recently booked a flight using a voucher with less than 24 hours notice and had no problems whatsoever.

One your ticket is booked by phone, you will need to bring your voucher in person, to any airport with a USAirways counter to redeem.