Hello,

> The models page (http://www.netbsd.org/Ports/macppc/models.html) has a 
> lot of "The internal modem is not supported yet" notes. Are these 
> modems going to be supported at some date? When?
> 
> The specific model I'm looking at is the revision B 300MHz iBook.

Find documentation and someone who has the right combination of time, knowledge and hardware. The newer internal modems ( like in my iBook G4 ) are braindead anyway so the main CPU needs to do all the signal wrangling - not quite trivial.
The older modems may just be connected to some serial port, these should work.

have fun
Michael