" Also I do not believe for a second that the helpdesk cannot dial out!" Unfortunatelt this is very true.
I work in a helpcentre ( not an NTL one ) and we manage / look after all the telephony systems and it can be set-up to restrict who can dial out and at what time tehy can dial out as well !
This is a standard set-up for call centres, although the sytstem can be cutomised to suit