Mitel BB424 - key expansion module for VoIP phone

The BB424 provides visibility over other users as well as single-button access to advanced telephony features including transfer, silent monitor and barge in. The BB424 is a USB accessory for the IP485g IP phone and features 24 programmable buttons. Users can also employ the four page buttons across the bottom to program up to 96 buttons total. If the user prefers seeing all the buttons at the same time, up to four physical units can be used instead (requires additional local power supply).