USRobotics NETServer/8 - Manual (Page 109)

Talking to the Modems 7-5
Keep in mind that other programs on the host may use these
pseudo-tty devices, but usually select the pseudo-tty drivers
from the beginning of the list (for example, /dev/ttyp0, /dev/
try, and so on). In order to avoid conflicts, we recommend you
select the pseudo-tty device drivers from the end of the list (for
example, /dev/ttypf or /dev/ttyqe).