Actually, I don't think a PIN message is all that secure. If you are on BES, your company can access your PIN messages if they decide to go looking. And if you are with BIS, I think PINS are actually only "regularly" encrypted, if that makes sense.
Here is a bit of info - recently, in Canada, PIN messages have been retrieved by companies if they feel their employees are sending sensitive info that way, and also can be retrieved by those who know how if just on BIS:
"PIN-to-PIN transmission security: PIN-to-PIN is not suitable for exchanging sensitive messages. Although PIN-to-PIN messages are encrypted using Triple-DES, the key used is a global cryptographic �key� that is common to every BlackBerry device all over the world. This means any BlackBerry device can potentially decrypt all PIN-to-PIN messages sent by any other BlackBerry device, if the messages can be intercepted and the destination PIN spoofed. Further, unfriendly third parties who know the key could potentially use it to decrypt messages captured over the air."
Security is not an issue for me, though. But if you are on BES and selling company secrets, trouble looms.