# Recommendation I.251.1 (11/1988): Number identification supplementary services: Direct-Dialling-In (DDI)

> superseded recommendation/international standard from the International Telecommunication Union

**Wikidata**: [Q26985369](https://www.wikidata.org/wiki/Q26985369)  
**Source**: https://4ort.xyz/entity/recommendation-i-251-1-11-1988-number-identification-supplementary-services-direct-dialling-in-ddi-