I have managed to get the D600's modem working on Mac OSX. Copy the Samsung D600 Modem file I have attached to this post to \Library\Modem Scripts of your startup drive. Now you need to go to Internet Connect (plug your phone in via USB cable) and get it to use that script. For the number and username/password you need to dial refer to your service provider (I'm with O2 UK, the number to dial is *99# and username and password are "username" and "password". Now you're set! Just press connect from Internet Connect and this should work! Email me if you've got a problem with any of the instructions...
Peace
Peace