An interference device and method of interfering with signals from a UMTS base station in a particular area are disclosed. The interference device receives a signal from the base station intended for a mobile device to initiate a communication session. The interference device synchronizes to the S-CCPCH and alters the TCFI and/or the data in the data field of the slot so that it is not longer correct. Time-shifted copies of the altered signal are then multiplexed and transmitted to the mobile device as a jamming signal. The jamming signal is received by the mobile device and causes the mobile device to be unable to determine the data of the original signal from the base station.