If you configure the interface on the router with an IP address in the correct subnet, and this is the default gateway for a device in the subnet, then they will ‘talk’ together with no additional configuration.
For example, if the interfaces are Fast Ethernet
ip address 192.168.180.254 255.255.255.0
ip address 192.168.181.254 255.255.255.0
Then configure all the workstations to use the .254 as the gateway, and it will all communicate together perfectly. Choose a different last address if this one is already used. I doesn’t matter if they are different, one is .254 and the other is .23 for example, just make sure this is used for the default gateway.
i am agree with that statment writen above
if you want to talk with other network you should install the VIOP network in your orgnigation.
for it you should contect with who provied the router service.
or you can config the intercom service for talking to you users