Optional Bluetooth module for system telephones for connecting Bluetooth 2.0 headsets. Up to 6 headsets can be registered per module (headset and hands-free profile support according to BDA), up to 18 headsets per communication system. The BT module 40 requires the current system firmware version at the time of delivery and is supported in the device types ST 40, ST 42 (IP) and ST 45 (IP).