Yes, assign the serial-port (COMPIM) in your schematic to physical port in your PC, set port name and baud rate correctly.
Connect a modem to your PC serial port,
in virtual terminal of serial-port you can send modem commands. Check your modem whether it accept text or PDU format for SMS, and send SMS commands according to correct format.
Hope this helps you.
Without connected modem or phone it's difficult. You have to input virtual-terminal every thing that output by a modem when it receives a SMS; and response commands.