PBX stands for Private Branch Exchange. It is a small telephone switch that companies use to save money. When a business needs several lines in the building to allow all of the employees to use the phone at the same time, a PBX is the best solution. It essentially allows the user to dial an access number to reach an outside available telephone line, without having to pay for all those separate phone lines. If you have ever had to dial a 9 to get a dial tone and start making a call, you have used a PBX.