What’s the Difference Between PSTN and ISDN Phone Line for Your Business?

It’s not until you need to sort out your phone system for your business that you realise that there are different systems available. Most people just think that there is a ‘phone system’ and that’s it.

Actually, there are a few systems available, but for phone calls, it comes down to either a PSTN or ISDN phone line for your business. There is not much difference in the costs between these two systems, but there is a big difference in the functionality.

PSTN (Public Switched Telephone Network)

This is the original phone system that we all recognise, where one phone number is attached to one phone line. Many people refer to it as POTS – Plain Old Telephone System – which lots of homes and businesses still use, but which is being phased out by the new NBN system.

This is the type of system you have in your home and is suitable for many home businesses, small businesses and sole traders. However, once you start to grow your business and need more than one or two different phone lines, then you should look at an ISDN system.

Just a heads up – PSTN lines are still needed for standalone systems, such as fax or EFTPOS machines, back to base alarms, remote access and ADSL2+ internet connections.

ISDN (Integrated Services Digital Network)

One of the main differences between these two phone systems is that PSTN lines are analogue and ISDN are digital. That’s why you can only have one number per single line with a PSTN system. With ISDN however, you can have anything from 2 to 30 different phone numbers that can all be run from a single line.

This system allows for up to 30 employees to each have their own direct dial phone number and if you need more numbers you can install a 2nd, 3rd or 4th ISDN line, each giving you an extra 30 numbers. Clearly, an ISDN system is much more functional for a medium to large sized business, because if you have 50 employees, you only need 2 ISDN systems instead of 50 PSTN lines running into your business.

Apart from the extra phone numbers, digital lines give you a much better voice quality and can also transmit images, data and video as well. This makes ISDN lines perfect for growing businesses who need as much functionality as possible in their phone system.

The bandwidth of ISDN systems is much better than PSTN systems, which makes it a breeze to hold voice and video conferences and to transfer large data files as well. This is the telephone line system used by larger businesses and is usually networked through the offices and departments using a PBX system.

Which system is best for your business?

Your decision really depends on how many phone lines you need to run your business efficiently. If all you need is a line for one single phone and another for your fax machine, then a PSTN system should be fine for your business. Once you start needing more than 2 lines, then it is only sensible to move over to an ISDN system.