OK,
Never let it be said that I don't admit when I'm wrong!
So, I have just spoken with our Licensing team and they tell me that you require the following:
Item #SW-001-4.0-AL01 Basic Station Audio connection to any internal party or device (phone, fax machine, or modem). Also required for remote station connections.
Item #SW-001-4.0-AL10 Interaction SIP SoftPhone Use the Interaction SIP Soft Phone on a general purpose computer, desktop or laptop, to make and receive station calls without a separate dedicated hardware endpoint. This software application includes a dial-pad and the capability to link with a windows sound device. This is a software part only - no hardware included with purchase. Requires a Basic Station License.
You live and learn...
HTH