V18 - Tried on both T42 and T46 handsets, its a RJ11 jack so I cannot test on a PCWhich 3CX Client/App are you using? Have you tried all three clients that are available for a PC (3CX Webclient, 3CX Desktop App and 3CX Windows App)? Do you have the same issue on all of them?
Also, have you tried a different headset which works or used the built in mic of the PC if it has one? Do you get the same behavior?
Founded in 2005, when VoIP was an emerging technology, 3CX has gone on to establish itself as a global leader in business communications.