I was an intern at RIM two years ago, and I was with a small team that was working on applications that used PIN messaging in some of the ways you're envisioning.

It never really launched in the way that it was being worked on at the time I was there, but little pieces did make it out in various other forms—I wrote the QR code syncing mechanism that was part of it, which I believe is now launched as a part of BBM.