However, if the host is AOL, Earthlink, or Speakeasy (which together cover close to 50% of all ISP users in the U.S.) the information on the DNS would give the required information (I just checked with all three). My suggestion is obviously not infallible, but compared to how much effort it takes to try, it is worth a shot.
AOL hosts domains for users? I didn't even know that... I know Earthlink does. I don't know about Speakeasy. But I'm pretty sure that the three of those wouldn't account for 50% of all webhosting. I suspect you are getting confused between webhosting and internet access.