Thank you sicelo! N9 doesn't have a PC Suite mode, instead it has a 'Sync and Connect' mode, which is what I used to use on Win 7 to use it as a USB modem. However, after I upgraded to Win 10, it has stopped working. All the drivers are installed, Win 10 detects it as a USB modem (I can see it in Device Manager) and when I try to connect using the dial-up connection already set up, it comes back with Error code 618 (port not open).

Any suggestions?