Many thanks, I managed to connect to the internet using a pppd line
like this:
/usr/sbin/pppd /dev/ttyS1 115200 debug user dwlee connect
"/usr/sbin/chat -v '' ATDT5472107 CONNECT''"

The only problem is that it does not set the default route
automatically, so I have to enter this line to make the internet
scautly work:

route add default ppp0

That does not bother me too much, but I want it to do it
automatically. Thanks for all your help!

Iguanaman