Ethernet pass through connector on bottom of IP phone. What do you reckon is inside?
Do you know what circuit is behind these 2 RJ45 jacks?


You can buy single chip ethernet switches with two twisted pair ports (i.e.. integrated phys) and a MII port designed for exactly this application. e.g.

http://www.microchip.com/wwwproducts/Devices.aspx?product=LAN9303

They are pretty cheap, especially when you consider that they are used instead of a phy chip. I would bet that such a switch chip is what is in the phone.


  that has a link to this circuit: http://www.zen22142.zen.co.uk/Circuits/Interface/pethhub.htm"


I highly doubt any reputable phone vendor would put a hack like that in their product. It's a clever trick but it is a major specification violation, is likely to cause major compatibility issues and only works for 10BASE-T.