[Asterisk-Users] How can I get a dialtone calling from outside...

[Wilson Pickett]

> Isn't that what you would call Direct Inward System Access?  Probably

FWIW, DISA is one of those concepts it is not easy to find without
already knowing the name, and if you know the name, you prolly know
what it is, etc.  The snake that bites its own tail. The only reason I
discovered it was because I read the available fledgling online
version of what is now the excellent O'Reilly Asterisk book about 20
times in a row, especially to find things I didn't get and try to
figure out what they were.