The CS500 series is setting a new standard for wireless desk phone communications. The new convertible headsets feature streamlined design, improved performance, and the same great reliability. Three comfortable wearing styles available: CS510 = monaural, CS520 = binaural, CS540 = convertible.* sold separatelyBinaural wireless headset, up to 9 hours talk time, up to 350ft range (depending on environment), use with Electronic Hookswitch Cable or Handset Lifter to remotely answer/end calls*, DECT technology provides better audio; eliminates interference from Wi-Fi networks