Internal roaming

An access control system for a wireless telecommunications system comprising: a first base station serving a first site and operable as part of a first wireless telecommunications network; a second base station serving a second site and operable as part of a second wireless telecommunications network; the first and second telephone networks being connected together, whereby a call can be connected between the first base station and the second base station via the first wireless telecommunications network and the second wireless telecommunications network; and the access control system comprising: a data link of which use is restricted between the first network and the second network, whereby a call may be connected between the first network and the second network; and a first site link access control unit comprising a database for storing identities of wireless terminals at the second site for permitting calls to such terminals made at the first site to be routed from the first site to the second site over the data link.