These are sometimes called digital lines are also used for voice. They come in pairs (ISDN2) and 8 – 30 (ISDN30). They are connected to digital telephone systems. The main reason for having ISDN is the use of a service called DDI. DDI is direct dial in, meaning that telephone extensions on a telephone system can have their own direct number.
These are the traditional standard lines. These can be used for making and receiving calls, they are also used for fax, pdq and very importantly are needed to run a broadband connection over. They can be connected to both analogue and digital telephone systems.
You do not need to use the same supplier for calls as you use for your line supply. This means that even if you are not able to move your lines to us at present you can still make savings on your calls.