This is probably a "geoport" modem, and the 9th pin, I believe is power.
It won't plug into the older machines, but should "work" with the proper
adapter, if the power requirement is otherwise met.

-dgl-

>Greetings, I want to set up my NetBSD machine for ppp.
>
>To do that I need a knew modem as the one I have has 9 (rather than the 
>required 8) pins.
>
>I have a little adaptor which will make a PC serial cable into a Mac one.
>
>So, if I were to buy this: <http://www.dabs.com/products/prod-
>info.asp?quicklinx=V7J> modem, would it work?
>
>There is so little information there, I know it's hard to say. But is 
>there a good chance that it would?
>
>Take care,
>
>~ Matthew