Plantronics W440-M SAVI Convertible, Wireless DECT Headset System for Laptop, Softphone & Multimedia Microsoft Lync Compatible - Unlocked Phone - US Warranty - Black & Silver Lightest DECT wireless convertible headset with noise cancelling mic to filter out background noise Multitask handsfree up to 300 feet from base Hot swappable battery for unlimited talk time Microsoft Lync compatible Voice dedicated DECT technology eliminates W-Fi interference Unlocked cell phones are compatible with GSM carriers like AT&T and T-Mobile as well as with GSM SIM cards (e.g. H20, Straight Talk, and select prepaid carriers). Unlocked cell phones will not work with CDMA Carriers like Sprint, Verizon, Boost or Virgin.