I have just built a Windows XP machine for a friend that includes a US Robotics 56K Internal PCI V92 Data/Modem (Part No USR805661A)
For several weeks everything worked fine but now for some reason the modem does not release the phone line when he disconnects from the Internet. The only way to make a phone call is to turn the PC off and unplug it from the wall. Only then is his phone line released.
In addition occasionally when he dials up the PC omits a police siren sound (seriously!) similar to the warning noise when a CPU fan stops for example.
I have scanned the PC with AVG Free, which gave it a clean bill of health.