Here are a few hints:

I followed the instructions here (in the faq-o-matic) for MkLinux PPP.
On my machine one change is required: the modem port is /dev/cua0 
not /dev/cua1 as it is on MkLinux.

Therefore set up as per Mklinux PPP instructions but first
do the following commands:
rm /dev/modem
ln -s /dev/cua0 /dev/modem

And make sure /etc/ppp/options has either /dev/cua0 and/or /dev/modem
in it (not /dev/cua1)

Then to create the connection issue the following
command:
pppd file /etc/ppp/options

I hope this helps.

kbhend@dogwood.tyler.wm.edu