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.

For some telephone exchanges, a strictly defined classification cannot be unified. Due to the different names of manufacturers, customs, regions, product positioning and other factors. So you don't need to pursue it too deliberately, just purchase the appropriate equipment according to your own use requirements.