Our receptionist needs to have the ability to answer the phone while moving around. The model of the phone is 7965. I looked around and bought the Plantronics-CS540 Convertible Wireless Headset at Amazon.com. However, it did not work. I meant I still could not answer the call or get a dial tone by pressing the button on the headset.
It turned out I also need the APC41 cable, PLUS a configuration change on Cisco Call Manager or Cisco IP phone if you have permission to do so. The change is to ENABLE "Wireless Headset Hookswitch Control".
The APC41 should support 7942G, 7945G, 7962G, 7965G and 7975G.