One of the best tools for getting ready to program the Protel LTS is a flow chart. Drawing call flow into a block diagram helps the system administrator to visualize the routing of calls, and it makes it easier to collaborate with the customer/end user to correctly identify their desired result.
Here is an example of a flow chart that illustrates the behavior of an inbound phone number based on certain conditions. Sketching out a diagram similar to this one saves a lot of programming time. You can present the proposed call flow to the end user on paper first before spending time programming something that the customer doesn't really want.