Yeastar Billing Application License - S50. With the robust add-on app on your PBX, you are enabled to allocate call credit, top up extensions, and conduct call analysis on the basis of statistics. Both prepaid and postpaid payment models are supported. Besides the regular call charges and statement reporting, the App also allows you to offer different tariff plans and delivering different service qualities for different types of customers. Also, for enterprises where cost accounting is vital, department manager can utilize the valuable tool to monitor phone usage of its subordinates, spot misuse, and enhance employee productivity.