If I was to set up a Cosy 131 at my shop to the general ewon account I have would the customer just have to plug their network cable into the WAN port? Assuming they have internet connection it should connect to Talk2M.
As long as what the cosy has as it LAN network does not clash with their giving it as a WAN address for internet then you should be fine. Example is the Cosy having a LAN subnet of 192.168.1.x and a WAN subnet of 192.168.1.x would not work.