In the late 60's I wanted to call my girlfriend for free across the country using tones. I looked up the phone company spec's in the college library. After fi

In the late 60's I wanted to call my girlfriend for free across the country using tones. I looked up the phone company spec's in the college library. After figuring out the tones needed I went into the EE lab and made a tape recording of an audio oscillator. Then to make a call I played the tape into the phone. Worked great.