"- Discount certificate -- save up to $100 on a Continental round-trip ticket: $25 off $175-$274 ticket, $50 off $275-$399 ticket, $10 off a ticket over $399"

The dollar off certificate, is that something I can use to book at co.com or is only call in or go to airport kind of thing?

Reason I ask is that I'm flying fairly soon and don't know when my Prestige Pack was coming. Wondering if OnePass can give me the ID # of these certs over the phone so that I can book my itinary now.