| Abbreviation | Definition |
|---|---|
| UCD | Uniform Call Distributor |
| UCF | Uplink Center Frequency |
| UCIU | Universal Inter-Connection Infrastructure Unit |
| UCP | Universal Communications Platform |
| UCS | Unified Communication Service |
| UCS | Unified Communications Service |
| UCTN | Universal City Telecommunication Network |
| UDC | Universal Digital Channel |
| UDLC | Universal Digital Loop Carrier |
| UDP | Up Down Pair |
| UDR | Usage Detail Record |
| UDS | Universal Directory Service |
| UEM | Universal Energy Management |
| UGC | UnderGround Communications |
| UI | Unnumbered Information (frame) |
| UIDH | Unique Identifier Header |
| UIQ | User Interface Quartz |
| UIT | Union Internationale des Télécommunications |
| UKTA | United Kingdom Telecommunications Academy |
| UL | UpLink |