Many distributors and now contractors are centralizing billing. This is a cost savings for the company and easy to represent in OASIS using the parent / child relationships. Contact lists are merged, allowing common contacts to be identified in the parent company. (Entries in non-parent companies will not merge).
Set up the Parent Company
Open the customer entry you want to use for the parent, Change the Active field to Parent (shown)
Set up Child Company
Open the child entry and select the parent company from the listing as shown below.