Did you try "kermit" for example to confirm you can talk with the modem
(e.g. type "atz" expecting an OK unless you've turned off such responses
on the modem).  Did you try enabling a tty entry and verifying the cable
type required (i.e. straight or null-modem)?  You may wish to use something
like "kermit" to confirm dial-out success too.  Once you're happy that the
underlying serial connection can be made, then the ppp configuring can
start... if I understand your current dilemma.  -- Ken