Just a tip: This method is NOT necessary, and could make things more difficult.
When I was using kppp to dial up (pre-dsl days
), I just tried every tty setting in the drop down list. Then, later I found wvdial, and that was really easy to use.
The question really comes down to 'how confident are you that ttyS1 (or whatever) is really your modem?' The answer to that can be a bit cloudy.