It differs from UK numbering, which originated as alphanumeric codes based on town names.

In common with most European countries, the trunk prefix 0 must be omitted when calling Irish numbers from abroad.

A migration to a standard format, 0xx xxx xxxx, is in progress; however, to avoid disruption, this process is only being carried out as needed, where existing area codes and local numbering systems have reached full capacity.

The area code, or prefix, is normally separated by a space, or less commonly, may be displayed in parentheses (brackets).

Numbers are usually grouped into easy to read clusters, separated by spaces or hyphens for ease of use.

Irish geographical numbering is structured on a regional basis and follows a logical hierarchy.

All mobile phones and some VoIP services also support the international E.164 number format, so a + may be optionally used instead of 00.

Irish premium rate telephone numbers start with 15 and are read in two-digit blocks e.g. 1550 is "fifteen fifty".

[2] Irish non-geographic numbers consist of two national prefixes and the international freephone service.

Where high volume 'bursty traffic' is anticipated, such as on-air radio competition lines, the first two digits of the phone number are always 71.

This allows the telephone network to manage traffic during number analysis, even before the call is routed.

Ireland's non-geographic numbers and pricing structures were simplified and old shared-cost prefixes were withdrawn on 1 January 2022.

This is to avoid disruption to essential health services during a time of high volumes of calls.

From August 2019, various telecoms providers announced price changes which took effect on, or just before, 1 December 2019, including Virgin Media Business, in2tel, Virgin Media, eir, Tesco Mobile, Three, Digiweb, Pure Telecom, 48 months, Sky and NUACOM From 1 January 2022 callers to the withdrawn prefixes receive recorded announcements.

Check which carrier a subscriber is using for each category of call: Special short codes are used to control various supplementary services offered by digital local exchanges.

These services were first introduced as PhonePlus in 1981, on the first generation of Alcatel E10 and Ericsson AXE digital exchanges used in Ireland, and were rolled out nationally throughout the 1980s.

(Codes are unique to Virgin Media Ireland and do not follow ETSI guidelines) The subscriber will either hear a tone or a voice message to confirm services have been set up or deactivated.

The telephone number changes in Dublin and Cork took several years to complete, as they were busier area codes with few available lead digits.

To minimise disruption simultaneous working was enabled, allowing old numbers to remain mapped and active for a run-in period of one year.

This was followed by recorded announcements which remained active for at least a year, advising callers of the number change.

[9] Until the early 1990s, the 03 numbering range was originally used for calls to Great Britain,[10] including the Channel Islands and the Isle of Man, with the Irish prefix 030 replacing the UK trunk code 0.