T53W VoIP SIP telephone, Wi-Fi 802.11ac, 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, built-in Bluetooth support, optional DECT support (requires adapter, SKU #YKDD10K) for up to 4 x W52H / W53H / W56H, add up to 3 expansion modules (sidecar / attendant console) SKU #EXP50, Opus audio codec support. Optional AC power supply, SKU #YKPSU1.