It has something to do with DSL getting standards. They are not using cap(?) anymore but are using DMT. Thats why a 675 wont work, a newer 678 will tho. The only reason a 675 will work is if the line has been grand-fathered in, if you upgrade your line or get a new one, you will have to use a 678 w/dmt. e-bay has 678's for around $70. Hope this helps. Dan All, I just got my (Cisco 678) DSL hooked up again (upon moving). I don't know the specifics, but there seemed to be some issue about Cisco 675 routers being incompatible (sp?) with the upgraded DSL that I now receive from Qworst. They sent me another router even though I did not request it. It was the 675 and for some reasons, it would not have worked with my set-up anyway. Anyone know more about why 640K might not work with a 675? uak