The only time this will not work is if you have your phone lines configured differently to the default.  So for example if you have the phone lines:

1. Set up on a ring group, queue or follow me configuration.

2. You are using our IVR service. 

3. If we have customised your phone lines for you when we set up your phone lines. 

If this is the case please contact our Support Helpdesk with the details of what lines you want the calls to divert to if busy or not answered as we will need to set this up on the back-end of your VoIP line configuration.