I replied to your mail last week, but my reply bounced, so here it is:
Routers can be represented by Nodes on a Westplan network drawing. You add nodes by selecting Network | Add Node from the main menu, and clicking on the position on the network drawing where you want to node located. You can connect it to other nodes by selecting Network | Add Link from the main menu menu, and then dragging a link betweeen two nodes while the left mouse button is pressed.
Nodes can represent any point that switches calls. This could be a PBX, a VoIP Gateway or a router. Usually, there is no benefit in adding routers to the network topology because they do not usually make routing decisions at a circuit switched level. Also, Westplan does not take account of data traffic – it just calculates VoIP bandwidth requirements.