Idea behind this project was for CRM (Customer Relationship Management) system contacts with the billing system and billing system contacts with provisioning system to provision the services and network inventory system as well to assign phone numbers or IP addresses, etc.

Second possibility could be that the CRM system itself contacts with provisioning system to provision the services and network inventory system as well to assign phone numbers or IP addresses, etc.

A billing system should be composed of a series of independent applications that, when run together, are referred to as the billing system. A good billing system should provide major functionalities with a depth of flexibility.