I haven't seen a good one that works with all of them. Its fairly easy to consume the individual services individually as there is .net examples for all of them. I would probably consume them individually any ways and then maybe extract a common interface if possible so that other popular webmail services could be added as needed.
Yahoo: http://developer.yahoo.com/addressbook/
Gmail: http://code.google.com/apis/contacts/docs/1.0/developers_guide_dotnet.html
AOL: http://dev.aol.com/article/2007/integrating_openauth_into_aspnet
Hotmail: http://msdn.microsoft.com/en-us/library/bb463989.aspx