Abstract: A step by step central office serving coin box subsets is provided with a link circuit which on initiation of a call from the coin box sub-set connects the line finder circuit through an auxiliary coin trunk circuit to the central office equipment. This is performed whether or not a coin has been deposited at the coin box sub-set. When the user of the coin box sub-set dials the auxiliary coin trunk determines whetherA. the call is charge or non-chargeB. if the call is charge whether or not adequate coinage been deposited.On this determination the auxiliary coin trunk is freed to serve another call. If the call is charge and adequate coinage has not been deposited the call is interupted by the link circuit. If the call is non-charge or adequate coinage has been deposited, the link circuit connects the line finder directly to central office equipment so the call may proceed.