TERM and Solaris Ports
Under Solaris, as with all SVR4 systems, there is no "getty" involved in the login process. Logins are now handled by the Service Access Facility, or SAF, and the ttymon process.
To use serial ports for callin and callout under Solaris, you must define the ports to be bi-directional using the Serial Port Manager available via admintool. After you have done this, ttymon will use the /dev/term/xx device entry for incoming calls. You should use the /dev/cua/xx device entry for outgoing calls.
If you study the man page for the zs (serial port) device on your Solaris system, you will learn that the device driver handles the interleaving of incoming calls on the /dev/term port and outgoing calls on the /dev/cua port at the driver level.
When TERM for Solaris runs, it will modify the stty (or termios) settings for the /dev/cua device it is communicating with. When TERM closes the /dev/cua device before exiting, control of the port is given back to the ttymon process. When an incoming call is detected by ttymon (via the modem carrier detect line), ttymon will set the stty settings for the /dev/term device and begin interacting with the user.
You will note that TERM does not interact with the login process at all. All of the interaction between incoming and outgoing calls is handled at the driver level. For more information, please see the zs and ttymon man pages, and the Solaris system administration chapters in the on-line Answerbook.