nine or ten digits after the 0 trunk code or +44 international dialling prefix. Four-digit area codes Four-digit area codes have either six-digit subscriber numbers or a mix of five- and six-digit subscriber numbers. (01xxx) xxx xxx This is the format used by most areas. It has a four-digit area code (after the initial zero) and a six digit subscriber number, and is known as 4+6 format. These area codes were changed by adding a "1" directly after the initial zero as a part of PhONEday in 1995. Just short of 581 areas use this format, and the area codes range from 01200 to 01998. Almost all (01xxx) area codes now have only six digit subscriber numbers, but a small number of these areas also have some subscriber numbers only five digits in length (see next section). Six of the four-digit area codes are known as "mixed" areas as they share those four digits with the twelve five-digit area codes. This leads to a restriction as to which initial digits can be used for subscriber numbers within those four-digit area codes, e.g. in the 01387 four-digit area code, subscriber numbers cannot begin with a 3 because 013873 is a separate five-digit area code; likewise in the 01946 four-digit area code, subscriber numbers cannot begin with a 7 because 019467 is a separate five-digit area code. (01xxx) xx xxx This is used for forty smaller towns which have a mixture of six and five digit local numbers, each type allocated in specific DE blocks*; e.g. in the 01647 area code numbers beginning 24 and 61 have five digits (24xxx and 61xxx; known as 4+5 format) whereas all other DE blocks* within that area code have six digit numbers. The number of places with five digit subscriber numbers and an 01xxx area code has declined rapidly in recent decades. There were 511 ranges allocated across 56 different area codes in January 1998. The Big Number Change removed many, especially in Northern Ireland, and by July 2005 there were only 329 ranges in 42 codes. By April 2010 this had reduced to 324 ranges in 40 codes, with still the same number in November 2012. The 40 area codes are listed in the table below. *A DE block is a block of numbers where (taking the area code and the subscriber number together) the initial 0 and the next six digits after it