The present invention is directed to a system and method for detecting impaired electric power equipment. The telephone station apparatus switches from a first communication line to a second communication line and initiates a call to the voicemail server. In addition, a technique to normalize the gains of the microphones based on people’s speech is presented, which allows aggregation of various audio channels from the ad hoc microphone network into a single stream for audio conferencing. A key switching transformation converts a ciphertext with respect to a first secret key and a first modulus to a ciphertext with respect to a second secret key and a second modulus.