There seems to be a lot of confusion around what a PABX is, what a PBX is and the difference between the two. Well there is no difference. A PABX is a Private Automatic Branch Exchange and a PBX is a Private Business eXchange. Both serve the same purpose and that is as a telephone system for a business. If your business is looking for a telephone system that is owned by the business as opposed to by a telephone company, then you are looking for a PABX system, although in most recent years these are often referred to as PBX Systems.
A PABX will connect the businesses instruments separately to the public telephone network (PSTN) A PABX system makes sure that every internal call made is routed through the PABX.