Why do you need such device?
I was looking for a way to configure a ADSL router to work with LAN cable. I've checked on a couple of forums and I understood that some ADSL routers, probably most of them, can configure each LAN port to work as WAN port. I really do not know how exactly I did it, but it can be done! It is possible to have ADSL router working with LAN cable.
Give me detailed instructions please, i'm trying to connect a wan line into an adsl modem as well.