The new University phone system has the ability to present “caller id” on external phone calls as the actual DDI number of the phone, rather than the generic university switchboard number. This makes it easier for people to call you back. Whether the number actually reaches the called party is dependent on a number of technical and administrative factors; at present it will work for most calls to UK landlines. Unfortunately it won’t work for most calls to mobile numbers.
The telecomms office is aware that some people are touchy about having their DDI numbers revealed, and is therefore enabling the facility for a department only when they have confirmed that they want it. Once the facility has been enabled, individual extensions can be set up to present either their own DDI number, or the generic number 01223 336633.
I intend to ask telecomms to enable the facility for Lab extensions on 16th August, at which point DDI number presentation will become the default. If you do not want your DDI number presented outside the University, please ask
email@example.com to change the setting for your extension.
As far as I know it is not possible to withhold DDI for a specific call.