Does anyone actually know anything about these devices?

Can a 2820 IPPBX be used just as an IPPBX on a LAN, and not be a router?

I am still just trying to test its PBX functionality, but I cannot get it to register a trunk. However, that may be because it can only register to a SIP server via the ADSL line and not via the LAN (which has its own other router already set up and running - actually a Vigor 2820).

So, can the IPPBX register via the LAN or must it be via the ADSL line?

I don't mind either way as ultimately it WILL be the router, but in the meantime, I need to know whether I can test it in this way or not. Anyone?

You can use WAN 2 to connect directly to an Ethernet connection and the IPPBX will work thought the LAN that way.

I am not an expert, but you will need to make sure that your router/firewall that is connected to the Internet will allow SIP connections.