T53 VoIP SIP telephone, 2 x Gigabit Ethernet, 8 x line keys, PoE required, AC optional, 3.7 inch backlit LCD, HD audio, RJ9 headset jack, EHS support for specific Jabra, Plantronics & Sennheiser wireless headsets via USB adapter, SKU #EHS40, 1 x USB, optional Bluetooth support (requires adapter, SKU #BT41), optional Wi-Fi support (requires adapter, SKU #YKWF40 or SKU #YKWF50), add up to 3 expansion modules (sidecar / attendant console) SKU #EXP50, Opus audio codec support. Optional AC power supply, SKU #YKPSU1.