I found (with some help from the AppleCare guys) a way to use my mobile phone to send and receive faxes over Bluetooth. The purpose is to add the Bluetooth modem port to the faxes list.
Here are the steps:
- In System Preferences, go to Print & Fax
- Open the Printer Browser (click "+" in the Printing tab)
- Option-click on "More Printers"
- Select "Advanced" in the popup list
- Select "Bluetooth-modem" from the "Device" popup that appears
- Select "Other" from the "Printer Model" menu
- In the "Choose file" dialog go to System>Library -> Frameworks -> ApplicationServices.framework -> Frameworks -> PrintCore.framework -> Resources -> English.lproj -> Fax.ppd. Note that you can replace English.lproj with the language of your choice.
- Finally, click Add

