I bought a couple off of ebay ( thats a PAIR of phones ) for about £25 ( includes postage)
Just go to ebay and enter usb phone and get pages!
Glad your thinking phone and not head set, tried that and felt a fool!
Yes mine a cheap plastic job, but it works well
Hope you have a usb port at the front, as delving behind is never Cool.
USB1 is fine, don't worry about insiting on usb2
And finally , try out Gizmo, very very new , but has its own forum and is open source.
You can run Skype and gizmo at the same time