Numbers I have found
Pen has 219U on the key
Library card left drawer 421287
Visa application right drawer 0023
Service number middle drawer 9820
Zune can take a ton of numbers so it's gotta be a combination of all or most of these sets
iPad only takes 4 but the pen code will not work at face value interesting to note to iPad is a phone dial so it's possible the pen code translates to a word hence the U is probably a hint