Phone-patching was a hip new skill late in the 1960’s. You saw it a lot on “Hawaii 5-0.” Hams liked doing it for the technical cachet, and they also liked it for how it streamlined health-and-welfare communication in time of emergency. It frightened public utilities a lot (which tells you about the number of people involved in amateur radio at the time). Patching radios to the telephone system was ultimately a good enough thing, finally, that it forced changes in law. North Carolina, Nebraska, and Oklahoma utilities commissions attacked in court savagely, carrying on a line of legal wrangling that had gone on since the Carterphone case in 1968, the opening battle of the phone companies’ war on customer-owned attachments. The FCC sided with hams, to many people’s surprise. Phone patching in principle was made legitimate by January of 1969, in most areas of the country. Floods of manuals appeared right away, that explained interface specs, and showed how to counterfeit phone company equipment. An example of this was a much-copied project to make a dynamic VU meter out of a Calectro voltmeter that would act just like the Western Electric standard ones. Commercial components sprang into existence almost as quickly. This is the Heathkit version, the ubiquitous ‘hybrid phone patch’, of which a couple variations exist. Hybrid and Phone Patch are redundant terms. The ‘hybrid’ part means a telephone circuit that interfaces with radio. This is an analogue type, that requires no more power than that which comes from the radio and phone circuits; there are digital ones now, that typically require power of their own.