In his mail John Newlin wrote :

> This is not an answer to your question, but...
> are you using chat to connect?  And if so
> can you send me your chat script, and the
> pppd command you are using to start it up?

I think the answer may interest some other people.

There are 4 files: 
ppp-on : the main script I launch.
pppopt : the pppd options (needed by ppp-on)
chatrun : the chat script (needed by ppp-on)
ZDXF2834 : the chat text (needed by chatrun)

ppp-on :
--------------------------
#!/bin/sh
# the line above is necessary
#

PPPD=/usr/sbin/pppd

PPP_DEVICE='/dev/tty00' 
PPP_BAUDR='57600'
PPP_CONNECT=' connect ./chatrun'


PPP_ARGS=\
$PPP_DEVICE' '\
$PPP_BAUDR' '\
$PPP_CONNECT

$PPPD $PPP_ARGS file pppopt
--------------------------

pppopt:
--------------------------
-ac -am -vj -pc netmask 255.255.255.0 defaultroute modem crtscts noipdefault
--------------------------

chatrun :
--------------------------
#!/bin/sh
# the line above is necessary

CHAT=/usr/sbin/chat
MODEM=./ZDXF2834

$CHAT -v -f $MODEM
--------------------------

ZDXF2834 :
--------------------------
'' AT&FM1$SB57600S30=0S6=1S11=120&E11 OK ATTD41746060 CONNECT ''
ogin: mylogin
assword: mypasswd
--------------------------

Be aware to set the scripts executable (chmod).

-- Francois Pays