Is Yahoo an Internet service provider?

Although Yahoo isn't an Internet service provider (ISP) in itself, this article explains SBC Yahoo - a dial-up ISP.

In order to use any of Yahoo's services, you must first connect to the Internet using an Internet service provider (ISP). Yahoo and SBC have partnered together to provide users in the United States with Internet service. For more information about SBC Yahoo DSL or SBC Yahoo Dial and to order a startup CD, please visit the SBC Yahoo website.  

For further questions regarding accessing the Internet, such as problems with your connection or what phone number to dial, please contact the ISP that you will be using from your location.