Question : Connecting 2 LANs, each with own DSL router, DHCP server, etc.

I am not completely clear on the method described here.

In my case, we have two separate LANs in a single office suite. Each LAN has its own ISP and router, DHCP server, etc. We now need the 2 LANs to be connected, in order to share an IP phone system, but need to maintain our separate LANs, ISPs, routers and, in general, keep the 2 LANs isolated from each other, except for the ports required for the phone system.

LAN 1 is 192.168.1.x
LAN 2 is 192.168.0.x

Does it make any difference which LAN is connected to the LAN port on "Router C" and which is connected to the WAN port?

Also, suggested routers would be helpful, as I do not think all routers let you choose between NAT routing and classic routing.

Thanks.

Answer : Connecting 2 LANs, each with own DSL router, DHCP server, etc.

Yes, every router I've seen will let you chose. Some manufacturers have different terminology.
For example, in some routers, turning off 'gateway mode' accomplishes the same thing as turning off NAT, etc.

Keeping the firewall enabled will make it a little trickier, but can be done.

Assuming you're not going to need a lot of bandwidth between the networks, then your basic Linksys/Netgear/DLink etc will work. If you need something with more horsepower look at their business-class routers.

Once the router is in place, the only other thing you'll need to do is to add a static route in each of the existing internet routers pointing to RouterC for the other network.