I have a "DualPhone" that I use with Skype.
Every time I start my computer - Windows Vista Basic - I have to select my
default sound device.
My options are: Speakers or USB Phone.
Initially, the sound that should be comming from my phone earpiece, comes
out of the speakers. If I change this to USB phone, my phone works fine but
all my PC sound also comes out through the earpiece. (Only when the phone is
off hook)

My daily trick now is to select USB phone. While I use my phone earpiece to
listen to say my voicemail, I change the audio device to PC speakers. Then
run a sound file to test and the phone then stays with its setting and the PC
sound comes out of the speakers..... I am then ready for the day...