The jabra gn netcom 0220 649 is a dual prong adaptor which expands the use of your headset to cover maine telephone systems by using the pj327 conversion plug it has a pj327 male connector at one end and a female rj9 connector at the other the pj327 conversion plug is an adaptor plug which changes the standard rj9 modular plug to the pj327 twin prong plug for use with avaya call master 3 and 4 handsets only