That's too bad;
There's a workaround: Write your own PIN messaging client, and use it as your own API. You will need the involvement of the BES server side, to relay the PIN's to the other BlackBerries. If it's possible to send PIN messages from a server to a BlackBerry?
Or maybe take advantage of METAmessage if it suits your needs:
http://www.blackberry.com/developers..._07_2004.shtml