This paper describes a new methodology for developing office automation-oriented private branch exchanges (OA-PBX). Business communications are closely related to the type of business, information used in the business, and the people working in that business environment. It is expected that business communications services, man-machine interfaces, and equipment will become significantly diversified and personalized compared to conventional telephone systems offering limited services. In the development of PBX's, which are expected to play a large role in the OA environment, how to rapidly and flexibly cope with diversified and personalized business communication needs must be considered. To precisely know the user's needs and to fully reflect them in products, it is necessary to introduce a new "quick-reaction" development methodology to replace conventional ones used for systems with limited services and long life cycles. This paper proposes the rapid prototyping of OA-PBX's and associated tools. A personal computer-based PBX prototype system with circuit/packet hybrid switching functions, which is used for evaluating system functions and services, is described. A new application-oriented specification language AIFLS (architecture independent formal language for switching service specification), and an automatic programming system APROC-1, which is a kind of expert system, are used for quickly and easily making software mock-ups of switching services and man-machine interfaces and are also presented here.