European Telephony Numbering Space
In the interest in forming a trans-Europe numbering plan as an option (or then future movement) for anyone needing multi-national European telephone presence, the ITU allocated country calling code +388 as a subdivided, catch-all container for such services. This was designated the European Telephony Numbering Space or ETNS.
Although some ETNS numbers were assigned, few phone companies supported connecting calls to ETNS.
Because of limited support, and the belief that the need for ETNS was superseded by URIs, ETNS was suspended in 2005 and abolished in 2008. All ETS numbers were cancelled by the beginning of 2010. The +388 code is scheduled to be reclaimed by the ITU at the end of 2010.
See also list of country calling codes.
Allocation area 
Geographically the +388 "country" code was an overlay on top of all the pre-existing, state-bounded country codes of the countries in Europe. Among "special" country codes, +388 was unique in that it was both supranational yet geographically bounded (other special codes, such as +881 and freephone +800, are completely international).
Instead of being subdivided geographically as in a typical numbering plan, the ETNS was intended to be subdivided by type of service or customer. It would therefore not have been possible to reverse engineer the location of an owner of an ETNS number based on the characteristics of the phone number. The numbers were also not allocated in blocks to individual carrier companies and were therefore intended to be portable. Carriers needed to have ETNS translation capability, or routing agreement with a carrier that did, in order for its customers to successfully call ETNS numbers.
Country Groups 
Specifically, ETNS was intended to be only one of a potentially larger set of European "country groups" participating in a shared regional overlay numbering plan. The only country group that comprised the ETNS was given an identification code of 3, which came after the +388 country code.
After the country group identification code, the number space was divided according to service, indicated by a European Service Identity code. The table lists the service designations (country code, identification code, and ESI code) available under ETNS:
European Service Identity codes 
- Public service application: 3883 1
- Customer service application: 3883 3
- Corporate networks: 3883 5
- Personal numbering: 3883 7
See also 
- European Radiocommunications Office
- ARCOME presentation: "ETNS project and corresponding field trial description"
- World Telephone Numbering Guide's information about European regional numbering