I have a TER-GX300 (07.03.301). The module works fine on a real COM port I have on my desktop PC, however when I switch to my laptop and use the USB->SER it doesn't seem to work fully. RSTerm crashes whenever I try to send an SMS.
I have baudrate set to 115200
Flow Control = Hardware
I have followed installation instructions USB_RS232_Cable.doc (found in CAB-ROU-232.zip)
My Prolific Driver Ver is 188.8.131.52 (updated to latest version after the version downloaded from your website didn't work)