iMobiMac beta offers BlackBerry tethering to Mac OS X
Speaking of tethering a smartphone to a notebook for use as a modem, it seems that there’s another way to tether a BlackBerry to your Mac. As we saw last year, this type of usage scenario commanded a nice bounty for a solution. The latest approach comes to us courtesy of UNEASYsilence who mentions that iMobiMac’s beta application allows for a DUN connection between your BlackBerry and your Mac. There’s a free trial of the beta but you’ll be limited to moving only 10 MB of data on your "new" Mac modem. Probably a good thing: too much data and the tether-police might getcha!
Related research and analysis from GigaOM Pro:
Subscriber content. Sign up for a free trial.

As with previous Bberry solutions, it seems your data is routed through a third party proxy. Something to keep in mind if you’re paranoid.
Dave is right, I have been invited into the beta program but once provided with the details have opted to not install it.
i have tested it and it does not use a third party proxy thank goodness!!! They will releasing another version soon to test