An Avaya PBX developer designs, implements, and maintains Avaya Private Branch Exchange (PBX) systems, a private telephone network used within a company. They configure and troubleshoot PBX telecommunications software, hardware, and IP networks to ensure seamless communication. They also develop and implement new features and functionalities, like automated attendants or call routing, to improve efficiency. Moreover, they often work with other IT professionals to integrate PBX systems with other business software. PBX developers also conduct regular system audits and performance tests to ensure optimal functionality, and provide technical support and training to employees.