Phone Lines

Analogue phone lines

An analogue phone line can handle a single phone call and have a single phone number. If you want to be able to receive multiple then it is possible to have several extra analogue lines, these would normally be referred to as auxiliary lines. So if you want to be able to receive six sales calls at the same time you would have a group of six lines all with the same phone number (one sales line with five auxiliary lines).

If there is a call in progress on the first line the second call will arrive on the second line and so on until all the lines are busy at which point any additional callers will get the engaged tone if they try and call you.

ISDN2e Lines

An ISDN2e line has two channels so it can support up to two simultaneous calls but has the advantage that it can have many different phone numbers. Once again you can have multiple ISDN2e lines with the same number range across all lines. If you want Six calls to your sales department then you could have three ISDN2e lines. Customers would be able to ring the main sales number which may ring all of the phones in the sales department, They could also dial a number that would get them directly to the sales person that they normally deal with. You could also have numbers for the service department, and the accounts department. No matter which number the caller dials as long as you have a free channel you will get the call. This is all possible because of the way that an ISDN line works. When you receive a call information about which of your number’s the caller dialled is passed from your line provider ie:BT to your phone system, your phone system can then decide dependant on it’s programming what to do with that call. The main sales number may ring all of the phones in a sales department or hunt round them one at a time, The sales manager’s direct number may ring his own phone and then the sales group if he is busy or doesn’t answer.

ISDN30 lines

ISDN30 lines are similar to ISDN2e but you can have up to 30 channels so 30 simultaneous calls. You have one ISDN 30 line installed and rent the channels individually. You usually need to start off with at least 8 channels to have ISDN30 installed. The main advantage of ISDN30 is that you can have up to 30 calls to one connection on your phone system. Most phone systems have slots that have line or extension cards plug into. A typical Line card would support 8 analogue lines or 4 ISDN2e lines (8 channels), if you needed to have 30 simultaneous calls that would take up four expansion slots in your system and mean purchasing four line cards. With ISDN30 just one slot will be needed leaving the rest free for extensions.

VOIP lines

VOIP is a protocol used to carry voice signals across data connections. It can be used to make phone calls via the internet provided that you have a sufficiently good and reliable internet connection with enough spare bandwidth for the quantity of calls that you want to make. Most new phone systems can be equipped with cards that enable them to connect to VOIP trunk providers via the internet. It is also possible to connect equipment to the phone systems analogue line ports or ISDN line ports that will convert the signals and enable you to connect to VOIP providers. You wouldn’t expect the quality to be as consistently good using VOIP via the internet but it should be possible to be at least as good as a mobile phone call.

GSM lines

It is possible to get a unit into which you install a sim card or multiple sim cards that allows you to make phone calls from the phone on your desk via a mobile network. The main reason that you would want to do this is to save money on the costs of calls to mobiles. These units can connect to phone systems either on analogue, ISDN or VOIP Line ports.


You can have a mixture of line types and the cost of making calls on the different types of lines varies dependant on the destination of the call that you are making and sometimes even the time of day. Most phone systems have the ability to make a decision on which line to route the call over based on the number dialled the time of day. This is called Least Cost Routing or LCR.

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