Telephone numbering plan

Greece has a national telephone numbering plan with ten-digit telephone numbers. The first digit represents the type of service. 1 is used for short codes, 2 for geographical numbers (3 and 4 are reserved for that purpose too), 5 is used for inter-network routing purposes (non-dialable codes) and VPNs, 6 for mobile services, 7 is reserved for universal access numbers (not active), 8 for reduced-fee services (like 800 toll-free, 801 local call, 89 dial-up and data services), 9 is used for premium rate services (901 for general purpose and 909 for adult-only services). All dialable numbers are ten digits, except for short codes (3–5 digits in the 1 range), 807-XXXX (seven digits) used for calling card access codes, and numbers in the 5 range, used for routing purposes and not dialable by end-subscribers.

A telephone number is the address of a telecommunication endpoint, such as a telephone, in a telephone network, such as the public switched telephone network (PSTN). A telephone number typically consists of a sequence of digits, but historically letters were also used in connection with telephone exchange names.

Telephone numbers facilitate the switching and routing of calls using a system of destination code routing. Telephone numbers are entered or dialed by a calling party on the originating telephone set, which transmits the sequence of digits in the process of signaling to a telephone exchange. The exchange completes the call either to another locally connected subscriber or via the PSTN to the called party. Telephone numbers are assigned within the framework of a national or regional telephone numbering plan to subscribers by telephone service operators, which may be commercial entities, state-controlled administrations, or other telecommunication industry associations.

Premium-rate telephone numbers are telephone numbers that charge callers higher price rates for select services, including information and entertainment. A portion of the call fees is paid to the service provider, allowing premium calls to be an additional source of revenue for businesses. Tech support, psychic hotlines, and adult chat lines (e.g. dating and phone sex) are among the most popular kinds of premium-rate phone services. Other services include directory enquiries, weather forecasts, competitions and ratings televoting (especially relating to television shows). Some businesses, e.g. low-cost airlines, and diplomatic missions, such as the US Embassy in London or the UK Embassy in Washington, have also used premium-rate phone numbers for calls from the general public.

Premium calls are typically independent of the caller's area code. These telephone numbers are usually allocated based on a national telephone numbering plan that makes them easily distinguishable from non-premium numbers; telephone companies often offer their customers the option to block calls from these number ranges, and in some jurisdictions, are required by law to offer blocking services.

E.164 is an international standard (ITU-T Recommendation), titled The international public telecommunication numbering plan, that defines a numbering plan for the worldwide public switched telephone network (PSTN) and some other data networks.

E.164 defines a general format for international telephone numbers. Plan-conforming telephone numbers are limited to only digits and to a maximum of fifteen digits. The specification divides the digit string into a country code of one to three digits, and the subscriber telephone number of a maximum of twelve digits.