FM telephone transmitter circuit
The FM telephone circuit is built on a PC board that is so small it can easily be fitted inside the housing of a telephone making it an instant pseudo-speak earphone.
This FM circuit connects in series with telephone line, steals power from it, and transmit at both sides of the conversation to an FM radio tuned between 90 and 95 MHz.
Source : http://radiofrequencycircuit.blogspot.com
