KX-DT590 Digital Expansion KX-NT505 IP Expansion 48 DSS Buttons to be used for Direct Station Selection Pre-Programmed One Touch Numbers Frequently Used Features Directly connected to the KX-DT543 or KX-DT546 Maximum of 4 units per phone 48 DSS Buttons to be used for Direct Station Selection Pre-Programmed One Touch Numbers Frequently Used Features Directly connected to the KX-NT553 or KX-NT556 Maximum of 4 units per phone Plantronics CS510 DECT Wireless Headset KX-TCA60 Wired Headset DECT Wireless Technology Lightweight 2.5oz Headset Hands-free Operation up to 350ft from Base Sleek Contemporary Design One-Touch Answer/End and Volume Control Noise Canceling Microphone Battery Lasts up to 9 Hours Adjustable Microphone 4 Foot Cord Clothing Clip to keep Cord out of the way Standard 2.5mm connection Back to the top.