Your modem is detected and installed in Control Panel / Modems, but RAS won't add it to the list.

If you run HyperTerminal, you receive:

HyperTerminal detected a general TAPI error

When you run Control Panel / Telephony, it doesn't.

All of the above sympoms can be caused by not have the Telephony service started.

Use Control Panel / Services / Telephony service / Startup and configure it to start Automatically.

Start the Telephony service.