Pre-Check is starting! Login and look for Opt-in box (was: coming later this year)
Just got off the phone with a CSR who was very helpful! Informed me that you just have to have the Know Traveler number in your profile before making the reservation. If you've already made the reservation, call them and have them remove and then re-add your frequent flyer number and your Known Traveler number will stick. He double-checked our new boarding passes (we're flying tomorrow) and confirmed the Pre-Check logo was showing. ^^^