The c2c links can be also added from the Settings\Numbers menu. The admin can create links which are pointing to either a user or a call group. They are used for different purposes, for example, to be placed on a "contact sales" web page, another link for "contact support" and so on. You may want to route the calls to a group to make sure that there is always someone available to take care of a visitor.
The admin can also add more links pointing to the same user. It is an equivalent of having multiple extensions - each for a different mapping. On an incoming call, the display name field will show the name of the c2c link that was used to initiate the call.