Well, the other thing you could do if it is only those ISPs is ban them (some examples):
mode # +b *!*@*.we.client2.attbi.com
mode # +b *!*@*.midsouth.rr.com
mode # +b *!*@*.comcast.net
mode # +b *!*@*.IP
Is that an EXTREME banning situation? Sure. Would it work? Most likely yes. Also, another thing you could do is:
mode # +b *!~*@*
Just some ideas for you to kick around if none of the above work. Also, Hammer, thanks for the REGEX method
