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.