It all depends on which CM you get on the phone I believe. The CM I got DID want our reservation number from Thompson. I found this on our payment invoices.
Other than that they'll ask you a few questions, like postcode, have you been before etc. Also, if you're wanting some of the more popular ADR's, like CRT, Chef Mickey's, Le Cellier etc then make sure you mention these first, that way you're more likely to capture them
Get them in order on your paper and then work your way down, that's what I did for April and it worked a treat! Another little tip, here in the UK it'll be 12 noon when the reservation desk opens. Call the number just before, it will give you the 'office is currently closed' talk, BUT, you have the number stored in the phone to just keep hitting re-dial until it takes you through to the menu

That way you should be one of the first through the day you call
Which are you thinking of?