Abstract: When zero on a telephone is dialed first by an unauthorized person hoping to establish a long distance line, a first blocking-spring (32) actuated by a boss (24) driven from the dial (17) arrests reverse rotation of a lug (28) before it can separate the signalling contacts (29,30) so that zero is not signalled but another digit is signalled instead. A second blocking-spring (41) is actuated by the boss as it returns to starting position for holding the first spring (32) out of engagement with the lug (28) so that a local number can be dialed.For normal operation of the telephone, a manually operable member (39) is moved into a position in which it prevents the lug-stopping actuation of the first spring.The telephone also can be set to prevent all outgoing calls while permitting incoming calls to be received.