Abstract: Test device (1) is for use in a test system for checking transmission procedures in a mobile telephony network. The test device (1) comprises a mobile telephone (2) configured such that it is able to communicate with a subscriber identification module (SIM). Furthermore, the test device (1) has a SIM simulation processor (4) associated locally with the mobile telephone (2), to prepare a SIM simulation which may be connected to other components of the test system. The test device (1) also has a physical SIM card (10) connected to the SIM simulation processor (4) such that the mobile telephone (2) is able to selectively communicate with the SIM simulation or with the physical SIM card (10). A test device (1) is thus provided, the use of which allows a greater flexibility of the SIM data used in the test process.