Note: The term “USB phone” is a misnomer.
USB phone sets are really only remote control and audio units for use with soft phones running on a personal computer. The soft phone is communicating with the remote VoIP server and doing the voice encoding and decoding, while the USB phone set provides a user interface to and headphones/microphone set for the soft phone running on the personal computer. USB phone sets also require driver software which may not be available for all operating systems. Check with the manufacturer before you buy!
Phone System 