Understanding every aspect of a phone system will help you make the best decision when you are ready to purchase and install. This knowledge will help you ask the proper questions, be able to recognize exactly what your business needs in a phone system, and facilitate a smooth relationship with the phone installer you hire. Let's start with trunking and analog trunk lines.
A simple analog trunk line is a telephone circuit made of copper wire that runs from your local phone company's central office building to your business location. The phone company's central office building houses switching equipment that connects you to the public telephone network. This is sometimes referred to as the local loop. Once installed, someone can call the phone number that you have subscribed to, and the phone company can connect the call to you through the analog trunk line. A good point to remember with analog trunk lines is that one phone number is associated with one line. If you need more phone numbers, then your phone company will have to connect more analog trunk lines to your business.
Trunking refers to the concept that many users can access the telephone network through sharing a set of lines instead of each receiving one individually. Think of a tree trunk: all of the branches share one trunk and through this connection are all granted access to the nutrients in the soil. Similarly, every phone extension in your office has access to the public telephone network through a smaller set of analog trunk lines.
If you have a small office, each telephone can be connected to the local loop and then receive its' own phone line. However, if your office is growing and you need to connect many phone extensions to the public telephone network, it just doesn't make financial sense to pay for separate lines to each phone. In most circumstances every employee does not need to be on the phone at one time. Instead, by using the trunking concept you can reduce the amount of telephone lines you pay for while servicing every phone in your business. In fact typical business phone systems are configured in ratios of 3-4 telephone lines for every 8 phone extensions.
If you are a small or medium size business looking to use up to 10-15 incoming telephone lines to connect your phone system, then choosing analog trunk lines would be a great place to start.