(from the project archive)
I wanted to install the option of an alternate Microphone for a Yaesu mobile radio which uses a modular (RJ11) type hand mic, whilst keeping the original microphone DTMF Functions.
I made this modification because I want to use the Headset from my Hand Held Transceiver, a Pryme SPM-1500 Throat Microphone, with my mobile unit for a hands free operation. This would also block out noice form my car stereo, or noise from other influences like a rolled down window.