However, it is not comprised of actual DTMF tones. This is clear because one of the two tones in the dialing sequence plays out a simple musical melody; actual DTMF tones are were chosen to be completely unrelated harmonically and so cannot be used musically.
I can play Mary Had A Little Lamb. Maybe you have to have a tin ear :-)
Of course, the Hotline ring sounds a lot different. It's "rough". Who made it? That's what I wonder. Was it considered artful, or was it just part of somebody's Foley repetoire. My feeling is that we'll never know.