3.5 mm and 2.5 mm diameter headset/headphone interfaces have been widely used in digital mobile terminals during recent years. Nowadays, the consumer is free to choose either the headset/headphone originally provided by the terminal manufacturer or other ones that are offered separately. However, the QoS/QoE perceived by users is influenced by both the electrical performance of the interface and the compatibility between the terminal and the connected headset/headphone. Recommendation ITU T P.MMIC specifies critical physical and electrical-acoustical characteristics for the universal headset interface with more than 4 terminals and provides corresponding test methods.