The circuit shown is only for analog telephone lines. I found it in Popular Electronics (1991). It takes the signal directly from the telephone line through a small output amplifier that can be obtained in old transistor radios. Power should come from batteries or supply since consumption is a little high to use a 9 V battery. The circuit can also be powered with 6V batteries as a power source. If source is used, it must have excellent filtration. An application is like "living voice" to ordinary phones.
