Abstract: Connection is made directly or via a switched telephone network between a tester and a telecommunication system to be tested. User data, such as voice signals, and signalling data, such as DTMF signals are generated by the tester to cause the telecommunication system to respond. The user and signalling data may be generated interactively to test the telecommunication system in real time, or by executing prerecorded scripts. When the tester is used interactively, the representations of the signals transmitted to and from the tester are recorded in at least one script file. Voice recognition is preferably used to determine whether the response received from the telecommunication system is the expected response, particularly when a script is executed. The vocabulary used for voice recognition may be created by repeatedly executing a script file (recorded during interactive operation of the tester or created manually) which causes the telecommunication system to generate the desired prompt(s) and message(s).