I too am suprised that it has no modem.
But here's another option, a USB Modem.
Get one, and get it working, then "BORROW" one of your outside lines and connect it to the modem.
THEN, with the Modem, dial into the system on another outside line and TRANSFER to *10.
-OR- Use a Desktop that has a modem and do the same.
-OR- as TOM suggests, use a DESKTIO that has a SERIAL PORT.
Those usually always have a serial port.