I dont think they are much in use anymore, but the term of it is "War Dialing", problem is u can end up with quite a high phone bill.
But there used to be some really good tools out for that kind of scanning.
/me thinks back to the days of 93 / 94
The use of "hacker" to mean "security breaker" is a confusion on the part of the mass media. We hackers refuse to recognize that meaning, and continue using the word to mean, "Someone who loves to program and enjoys being clever about it."
"Its not a bug, its a feature" (Epic Games)