Telephone dial tone frequency
Channel: emactan
Date: 08/12/2009

I've measured the dial tone several times and earlier the peak was at 440 to 450Hz. At end of the video the 400mV amplitude that I mention is of course peak-to-peak voltage.  Note that frequency spectrum may vary for various countries. US dial tone for instance consists of a combination of 350 and 440 Hz signals.

See http://electromotiveforces.blogspot.com/2009/12/telephone-signals.html for more