In this scenario we need a line with at least two subscriber numbers.  This example has three numbers; the third number may be used by the PC to identify itself for outgoing calls.

The number belongs to the line, but is used by the device for filtering purposes.

This example also demonstrates a technique to stop a device from answering incoming calls. In this example, the PC is not running any programs that will answer incoming calls.

Let us assume now that the PC is running a program that answers incoming calls. We have no means of stopping the program, but we don't want it to answer any incoming calls. If we configure the PC to answer calls to 9999, the PC will never answer a call since this number will never be offered.

In practise, if you don't configure a Called Party Number filter, a device will not apply any filter on this information and answer the call provided it passes any other configured filters.