The market for business telephone lines in the UK is dominated by BT, sold through their retail services division and BT Openreach, which supplies wholesale services to other service providers.  BT supplies three main types of line, single analogue lines, ISDN2 and ISDN30 digital lines. ISDN stands for Integrated Services Digital Network.

The simplest service is the single analogue line which is suitable for calls, fax machines, PDQ terminals, dial up modems and broadband connections. A single analogue line will provide a user with the ability to make or receive one call at a time. If you need to handle more than one call simultaneously, you can purchase additional analogue lines or a multi-line as your business grows.  Sales of analogue lines are very healthy mainly due to the phenomenal growth of broadband. At the moment most broadband services require a single analogue line to operate on, as internet traffic is carried over the copper wire to the local exchange and onward to the public Internet via your Internet Service Provider’s network.

Most business service providers also deliver a digital service for small businesses called ISDN2.  ISDN2 supplies 2 digital channels per line allowing the user to handle up to 2 calls simultaneously. Both digital channels can be utilised for voice calls, or one of the channels can be used for a fax machine. Alternatively both channels can be combined to create an Internet connection with a maximum speed of up to 128 Kbps in both directions. Believe it or not this provided a marked improvement on traditional 56.6 Kbps dial up Internet access before the emergence of broadband. ISDN2 is also a popular service to connect video conferencing equipment and applications, though sales of ISDN2 lines for this purpose are in decline due to the growth of broadband and web based conferencing services. Like analogue lines, additional ISDN2 lines can be added and configured by your service provider as your business grows.

For most businesses in the UK requiring 8 lines or more, ISDN30 has been the digital communications workhorse for decades.  It’s been around for a long time for a good reason; reliability. ISDN30 is a proven, resilient, digital service which supplies a maximum of 30 channels, allowing a business to make and receive up to 30 calls at any one time. Like analogue and ISDN2 lines, additional ISDN30 lines can be installed to meet increased capacity requirements. However if you need less than 8 channels, this is equivalent to 8 single lines, ISDN30 might not be cost effective as you must order a minimum of 8 channels.