Telephone numbers in Switzerland are defined and assigned according to the Swiss telephone numbering plan administered by the Swiss Federal Office of Communications. The plan has been changed several times and the most recent reorganization was implemented in March 2002. Plan of 2002 The Swiss telephone numbering plan implements the ITU-T recommendation E.164 and is designated E.164/2002, based on its last major revision in 2002. It is a closed numbering plan, which means that all telephone numbers, including the area code, have a fixed number of digits. Swiss area codes are officially termed national destination codes (NDC). A complete telephone number consists of ten digits: . Two formats are distinguished: three digits for the NDC and seven digits for the subscriber number, and four digits for the NDC and six digits for the subscriber number. However, a few exceptions exist. The associated dial plan requires that all numbers, even for local calls, must be dialed with the assigned NDC, in contrast to previous plans. When dialing from within the country, a prefix 0 must be dialed. The plan was amended a few times, e.g., the transition of numbering zone 01 into 044 and 043. National destination code The national destination code (NDC) is the area code for Swiss telephone numbers. Within Switzerland the trunk code 0 must be dialed before the NDC, while it is not needed from international locations. Telephone numbers are portable between numbering zones (ZN) or between mobile operators, and therefore an NDC does not imply that a caller is actually located in a particular zone or is serviced by any particular mobile operator. For landlines it is now merely an indication of the region where the number was originally attributed to a subscriber. The national destination codes are the following. 21 – ZN Lausanne 22 – ZN Geneva 24 – ZN Yverdon, Aigle 26 – ZN Fribourg 27 – ZN Valais/Wallis 31 – ZN Bern and surrounding areas. 32 – ZN Biel/Bienne, Neuchâtel, Solothurn, Jura 33 – ZN Berner Oberland 34 – ZN Region Bern-Emme 41 – ZN Central Switzerland (Lucerne, Uri, Schwyz, Obwalden, Nidwalden, Zug) 43 – ZN Zurich 44 – ZN Zurich (formerly 1) 51 – rail telecommunication networks (SBB CFF FFS) 52 – ZN Winterthur, Schaffhausen 55 – ZN Rapperswil 56 – ZN Baden, Zurzach 58 – business telecommunication networks 61 – ZN Region Basel 62 – ZN Region Olten–Langenthal (Oberaargau)–Aargau-West 71 –