DDD：Domestic Direct Dialing，国内直拨电话业务。关联词：IDD
DDI：Direct Dialling-In，直接拨入
DECT：Digital Enhanced Cordless Telecommunication，数字增强无绳通信
DID：Direct Inward Dialling，直接拨入。关联词：DOD
DOD：Direct Outward Dialling，直接拨出。关联词：DID
DTMF：Dual Tone Multi-Frequency，双音多频
