Recommendations E.163 E.163 was the former ITU-T recommendation for describing telephone numbers for the public switched telephone network (PSTN). In the United States, this was formerly referred to as a directory number. E.163 was withdrawn, and some recommendations were incorporated into revision 1 of E.164 in 1997.
Recommendations E.163 E.163 was the former ITU-T recommendation for describing telephone numbers, for the public switched telephone network (PSTN). In the United States this was formerly referred to as a directory number. E.163 was withdrawn, and some recommendations were incorporated into revision 1 of E.164 in 1997.