These are based on the secret slider mechanism that I blogged about previously.
I think they turned out pretty great! When you pull on the tab (handily labeled "pull" as I had noticed that some people, when handed the card, didn't really know what to do with it), the secret window is revealed, the apple and phone-a-thon sign pops up unexpectedly and the Gresham Barlow Education Foundation logo appears on the pulled tab.
(For more about their phone-a-thon and the foundation in general, check out the Gresham Barlow Education Foundation website! The Phone-a-Thon starts on February 23rd)