Abstract: A method for handling a call coming via a digital transmission system in terminal equipment suitable for speech and data service, the transmission system including at least one connection element which is a speech transmission connection when the call is in speech service mode and which is a data transmission connection rate-adapted in compliance with the CCITT recommendation V.110 or in a like manner and preferably attached to V.24 interfaces when the call is in data service mode. The terminal equipment starts the connection in speech service mode and automatically changes over to data service mode and initiates a procedure for changing the at least one connection element to a data transmission connection upon receipt, in speech mode, of a predetermined audio signal from the connection. The method can make use of a mobile telephone.

Abstract: A communication system in which terminal equipments capable of both voice and data service are interconnectable through a full-duplex connection or leg rate-adapted in compliance with CCITT V.110 or in the like manner and arranged to be attached V.24 interfaces, and to a method for controlling the connection. To enable the use of terminal equipments for both voice and data service in conjunction with such a rate-adapted leg, adapters provided at both ends of the leg utilize V.24 status signal states in the leg for hand-shaking end-to-end signalling events between the terminal equipment.