Armored Inmate Phone [JP-3500]

This is the be-all and end-all for phone transmitters. I use these in all the phones I work on, and the transmission quality and volume is loud and crystal clear. I can use early telephone equipment daily, and no one on the other end is the wiser, nor are they subject to any audio that could ever be guessed to not be from finest quality modern phone, when these transmitters are installed in vintage equipment.