A wireless headset allows you to walk around and talk up to 120m away from your desk telephone or computer. It is useful for people who need to multi-task. However, just using a wireless headset does not allow you to answer a call when you are away from your desk. For this you need remote answering.
Remote answering means you can answer a call while away from your desk. To get remote answering with your wireless headset you either need an extra cable or a handset lifter. The cable is called an EHS cable or electronic hook switch cable. Jabra, Sennheiser and Plantronics manufacture these for the most common types of telephones. Such as Avaya, Alcatel Lucent, Polycom, Panasonic, Yealink, SNOM, Aastra, NEC, Nortel, Toshiba, Mitel. You need to check the phone type.