Please edit /etc/ppp/chat/isp 
Insert your ISP's phone number,
username, and password.

Make a symlink in your /dev directory
to the appropriate ttyS for your modem
for com1:  ln -s ttyS0 /dev/modem
for com2:  ln -s ttyS1 /dev/modem
for com3:  ln -s ttyS2 /dev/modem
for com4:  ln -s ttyS3 /dev/modem

Use pon initiate a ppp connection.
Use poff to terminate a ppp connection.

Read the man pages on ppp and chat
for more information.

In some cases, perhaps an internal 
modem on a non-standard port, 
ln -s ttyS04 /dev/modem might work.
