For a dial-out system, you can create an /etc/ppp/options.ttyname file for the serial port with the modem, or choose not to use /etc/ppp/options.ttyname.
Solaris PPP 4.0 does not require an /etc/ppp/options.ttyname file to work correctly. A dial-out machine might have only one serial line for PPP. Furthermore, the dial-out machine might require few options. You can specify any required options in another configuration file or on the command line.