Haven't done much on the Samsung systems, I found this link - http://www.rocom-nimanssupport.co.u...install_an_OS7030_with_Slave_cabinet.pdf is that pretty much what is required to connect a 2nd box.

I tried an analogue phone and could make a call, but the extension didnt ring when the main number was called and I could't see a way to assign an extension number to the analogue phone. What have I missed.