There was MF and there was DTMF, each used a separate set of frequencies. MF was for in band signalling between switching centers (trunks) while DTMF was used for in band signaling from a telephone set to the switching center (lines).
Larry N. said:Actually Tom, MF (as used in the U.S. telephone industry) was not the same as Touch Tone?, though TT was also using a pair of tone frequencies, so the principal was the same and it was a form of multifreq. MF was used between central offices, and otherwise internally, but not out to the customer loop. I suspect the same tone differences were used in the UK, too.
Oops, hadn't spotted your post, Ned. DTMF was, indeed, what was trade named Touch Tone?.
Lou Schneider said:TouchTone was the same as the MF inter-exchange routing tone pairs except each frequency was slightly offset. You could tweak the inductors in a standard DTMF keypad to produce the correct inter-exchange tones and you were almost in business.
You also had to create an access tone that was different than the MF tones to get into the routing equipment. One hacker discovered the peanut whistle included as a prize in Capt'n Crunch breakfast cereal boxes could create that tone, and the rest is history.
Actually it was named "DTMF"Tom said:LOL Lou. Actually, it was two tones, one representing the horizontal numbers on the keypad, and the other representing the vertical numbers. Thus the term "multi-frequency".