Nothing new here...
I setup a new mobile for a user and to make sure ActiveSync was picking up contacts, i took a quick look in the address book app.
And there it was, clear as day.....The first contact, "Mrs Abbey Pin" who, mysteriously, only had a 4 digit phone number.
At the very least, make it look like a real number and then make the first or last 4 your PIN...or better yet, just remember it. How hard can it be?