Many businesses have multiple offices. Whether separated by large geographical areas or by several floors. Depending on whether there are numerous employees at each office, it may be necessary to provide a ComPBX to each office.
Multiple ComPBXs' in multiple offices are able to work in together and is recommended in situations where there is a large employee base (usually 15-20+) in each individual office. This is highly recommended if offices are separated by large geographical margins (e.g. 3 offices with 20+ personnel located in Melbourne, Perth, and Brisbane - it is highly recommended that there be 3 separate ComPBX's).
The beauty of multiple Hosted PBX's is that they can be configured to work together flawlessly. Almost every ComPBX feature can work between offices (e.g. conferences can be held between offices, calls can be transferred from one office to another, employees can call each other free of charge, and more).