The entire telephone number used to phone a subscriber on a telephone system consists of the basic telephone number and a number in a telephone number block. If the telephone number block is single digit, the direct dial numbers can be 0 - 9. The entire telephone number can then be for example:
The direct dial number 0 of often used as a direct number to the switchboard. Single digit telephone number blocks allow up to ten successive direct dial numbers. Likewise, two-digit blocks can address up to 100 terminals, and three-digit blocks up to 1,000 terminals. The telephone numbers in an assigned telephone number block can be managed and used within the telephone system completely at your own responsibility.
The telephone number block is typically ordered from the telephone service provider. Here it is important to order an adequately sized telephone number block straight away. This ensures consecutive direct dial numbers can be continued in future expansions.