Guide to Different Types of Business Phone Line

With all the different types of phone lines available to you today, it’s hard to know which one is the best choice for your business. In this article we will explore all the options on the market.

PSTN (analogue copper lines)

PSTN stands for Public Switched Telephone Network and this routes calls through traditional copper lines. Although these types of system are still used by many businesses today, they are slowly being phased out by a lot of providers in favour of internet-based phone systems.

This issue with traditional copper lines is that they only allow for one call to happen at any given time. This means that if you are on the phone and you receive another call, that caller will just hear an engaged tone or will go straight through to your voicemail (if you have this feature).

ISDN (digital lines)

ISDN (Integrated Services Digital Network) allows for larger data files to be sent and also provides better quality voice calls. There are two types of line that are typically used for businesses. There is not a huge difference between the two, the only difference is the number of lines the system will allow you to have.

ISDN2 – often used in small businesses, this will allow you to make two calls at the same time.

ISDN30 – this is for larger businesses and allows up to 30 lines. You benefit from fast connection, clear communication and your team will have access to DDIs.


This refers to a group of analogue telephone lines that share a phone number. One line is the main exchange line and the extra lines are known as auxiliary lines. The auxiliary lines are added to the mainline. This means if you receive a call while your team are on the line, the call will be routed through another line.

SIP Trunking

A SIP (session initiation protocol) trunk will be connected to your broadband connection and will allow you to replace your traditional phone lines to route calls through the internet.

How do you Know Which Type of Line is the Best for your Business?

There are lots of factors to think about when choosing the right phone line for your business.

You will need to think about how many employees you currently have and how many you plan to have in the future, the size of your business and how big you want to grow. As well as thinking about the industry you work in (some industries may require more phone lines than others). Traditional PSTN copper lines are being phased out by a lot of suppliers and even BT are planning to shut off all the traditional phone lines by 2025. This means they are not the most future-proof option for a growing business.

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