Re: NY Times Reporter Seeks Info About History of the SIT Tone

What is this tone? Is this the three tones when you reach a bad number?

The following website has some information:

The situation of "intercept" for when someone dials a non-working number was recognized at the very beginning of dial service. In panel switching, calls were routed to an intercept operator who checked into. The dialed number may not be assigned at all or been reassigned.

Dial PBX switchboards had separate appearances for intercept calls, distinct from dial 0 attendant calls.

The Bell System gradually automated this function. The first was a recording to ask the customer to dial again, but remain on the line for an operator. This would handle most errors in dialing and allow the intercept operator to serve changed numbers.

Then computers enabled storage of vocal digits in a natural way to automate the whole process so the entire process was automated.

Actually, they attempted to automate recorded and playback voice many years ago using a drum with motion picture sound film (using the sound track). Each track had a digit on it and the proper tracks would be selected. One use was for dial-to-manual exchanges to announce the incoming number, instead of using a lighted panel. Another was to return routing information. I don't think either application got very far with the technology available at the time.

We had a Bell recording announcement machine, controlled by a keyset, and it was large. I believe the recording was held on some sort of drum that rotated. Considering the heavy playback and low maintainence, plain recording tape couldn't be used as it would soon wear out.