At the beginning, the primary advantage of PBX was to save the consumption of internal calls: to process the internal line conversion of the system to reduce telephone charges. When PBX gradually became popular, some new functions were added, such as intelligent line finding, user calling, and dialing extensions, which were not provided by telephone companies.

The difference between the PBX and the group telephone system is that the users of the group telephone system need manual operation to dial the external line, while the PBX automatically completes this task. The hybrid system includes the functions of the above two systems.