It is possible to connect a University VoIP phone to the phone system from outside of the University, provided you are connecting it to a University-configured Remote Access Point (RAP).
In order for this to work, you will require a Cisco VoIP handset configured by the Telecoms Helpdesk along with a power brick and a RAP supplied by the University Wireless Service.
The RAP must be connected directly to your home broadband router via an Ethernet cable and the VoIP handset then plugs into a port on the back of the RAP to provide access to the University phone system.
This will allow your VoIP handset to connect to the University network and, in turn, the University Telephone System; allowing you to make and receive calls as if you were sat at your desk within the University.
The RAP will then also give you access to the eduroam WiFi network whilst you are within range of the RAP.