RETRO-M is designed to replace existing Home Intercom Systems and operate on existing 3 and 4 wire systems. BLUETOOTH you music by adding the BT-RECEIVER. No need to remove existing master wall housing, trim plates available to cover those large holes. The RETRO-M intercom unit has a built-in AM/FM radio. Plug in mp3 players such as iPod, iPhone, Zune or any other hand held player into the master and share your music with the entire family. Choose between two music sources; listen to the radio in one room and the mp3 in another room.