Actually I carry all the airline FF cards I have (even though I'm only elite on CO) when I fly. Once in Irregular Ops I was able, while in line for customer service, call up the other airlines and get all sorts of information because I had their phone numbers handy on the cards so by the time I got to the agent I was able to tell the agent exactly what flights were available on what airlines and what I wanted to do. This was before the age of PDAs and smallish computers, so maybe I don't need to carry the cards anymore, or I could just have an address book with the phone numbers. But I do think if you don't carry the cards, you want to have these numbers handy in irregular ops so that you don't ever rely on the agent to tell you want is available.