The Plantronics AP-1 is a hookswitch module that enables a CA40 user to place or receive a call without the need to lift the handset, thereby eliminating the need for the HL10. This module is compatible with Siemens Optipoint 500 basic, 500 standard, 500 advance & 600 office telephones. Please note that is only for use with the Hi Path PABX.