Landline Phone Dial Tone North American for 12 Hours
The modern dial tone varies between countries, being a "buzz" of two interfering tones (350 Hz and 440 Hz, as defined in the Precise Tone Plan) in the North American Numbering Plan (most of North America), and a constant single tone (425 Hz) in most of Europe. Modern UK dialling tone is also 350 plus 440 Hz.
http://en.wikipedia.org/wiki/Dial_tone