I have a customer who has a large network spread over several sites across the uk. the network addresses are ***.***.155.1 & ***.***.161.1

The system is on 161.50, I can ping it locally and all is ok, however i cannot ping it from 155.1. I can ping 161.100 (laptop) from 155.1 and vise versa.

I can use manager from 161.100 but not 155.1, any ideas

Do you have a correct IP route built on PBX to get back to originating subnet?

I have not done much with ip routes. What do I need to enter in the ip route table?

Umm...
***.***.155.0 as address along with the appropriate gateway and interface. Have you inquired with the installing Business Partner?

Also, does the customer have the routes built on their side to connect the 2 networks?

If you can ping your laptop on the subnets, then the router is routing.

Yes, you will need a route like:
***.***.155.0
255.255.255.0
***.***.161.X
LAN1 (assuming that is the LAN port that you are connected to.)

Where "X" is the gateway IP of that subnet.