Cvk488 backstage telephony system intercom, a set includes two headphones, a GSM box, a manual, the first use needs to activate the 488 GSM box, GSM box support mobile and Unicom SIM card, temporarily do not support telecommunications. The advantage of the cvk488 backend telephony system is that the headset can be 10 meters away from the GSM box, and the headset is a pure digital headset, without any noise and current sound. Very quiet, to restore the voice to 100%.