When David gets back home to change his school grade, he tells Katheryn that he is dialing into the school computer. Hear how many digits he dialed? I heard up to 22 digits dialed on his keyphone and the standard dialing back in the 80s was long distance (1) and 10 digits.
When you use dial-up modems, you sometimes have to insert pauses to allow for handshaking and password authentication. I can remember inserting 8 pauses for a connection I made from our hospital to our medical supply office. That might explain the 22 tones you heard.