Abstract: A gateway (11) is arranged to control the routing of a telecommunications call such that it may be handled in one of two or more alternative modes (3, 4). The gateway (11) identifies the intended routing of a call by way of the PSTN, for example from the dialed digits, and selectively forwards calls either to the PSTN (3) for control by a gatekeeper function (5) that attempts to route calls by another mode such as a packet switching network (4). By inserting the gateway (11) between the originating PBX (10) and the PBX (3), minimal alteration to the existing installation (10) is required.