Information Service Provider: A company which gives information over the phone in response to touchtones entered by a subscriber. That information may be weather, stock quotes, horoscopes, etc. Often it is a 900 number, in which a phone company will bill the end user for calls to the ISP (Information Service Provider). In many states, ISPs also use special local access numbers, that often begin with 976.
Of course, you could just use a voice portal like TellMe for free now.