| T1 | dedicated phone connection supporting data rates of 1.55 Mb/s |
| T-1 | North American Commercial Digital Transmission Standard |
| T3 | dedicated phone connection supporting data rates of about 43 Mb/s |
| TALI | Transport Adapter Layer Interface |
| TAPI | Telephony Application Programming Interface |
| TAPS | TETRA Advanced Packet Service |
| TAT | Terminating Access Trigger |
| TAT | Termination Attempt Trigger |
| TAT | Transatlantic Telephone Cable |
| Tb | Terabit |
| TBD | To Be Determined |
| Tbps | Terabits Per Second |
| TC | Temperature Coefficient |
| TC | Tandem Connect |
| TC | Technical Committee |
| TCAM | Telecommunication Conformity Assessment & Market Surveillance Committee |
| TCAP | Transactional Capabilities Application Part |
| TCB | Transfer Control Block |
| TCE | Thermal Coefficient of Expansion |
| TCIF | Telecommunications Industry Forum |
| TCK | Test Clock |
| TCM | Time Compression Multiplexing |
| TCO | Total Cost of Ownership |
| TCP | Transmission Control Protocol |
| TCP/IP | Transmission Control Protocol/Internet Provider |
| TC-PAM | Trellis Coded-Pulse Amplitude Modulation |
| TCXO | Temperature-Controlled Oscillator |
| Td | Decomposition Temperature |
| TDD | Time Division Duplex |
| TDM | Time Division Multiplex |
| TDMA | Time-Division Multiple Access |
| TDMDSL | Time Division Multiples Digital Subscriber Line |
| TDOA | Time Difference Of Arrival |
| TDR | Time Domain Reflectometer |
| TDR | Transaction Detail Record |
| TD-SCDMA | Time Division Synchronous Code Division Multiple Access |
| TD-SDMA | Time Division-Synchronous Code Division Multiple Access |
| TE | Traffic Engineering |
| TEAM | Transport Element Activation Manager |
| TED | Traffic Engineering Database |
| TEM | Telecommunications Equipment Manufacturer |
| TETRA | Trans European Trunked Radio |
| TF-A | Task Force A |
| TFD | Toll-Free Dialing |
| TGA | Thermo Gravimetric Analysis |
| Third-Generation | 3G |
| THz | Terahertz |
| TIA | Telecommunications Industry Association |
| TIG | Technical Implementation Group |
| TIMS | Transmission Impairment Measurement Set |
| TINA | Telecommunications Information Networking Architecture |
| TINA-C | Telecommunications Information Networking Architecture Consortium |
| TIPHON | Telecommunications and Internet Protocol Harmonization Over Networks |
| TIS | Total Isotropic Sensitivity |
| TIWF | Trunk Interworking Function |
| TL1 | Transaction Language 1 |
| TLA | Technical Live Advisor |
| TLDN | Temporary Local Directory Number |
| TLS | Transport-Layer Security |
| TLS | Transparent LAN Service |
| TLV | Tag Length Value |
| TM1 | WCDMA Test Signal |
| TM5 | HSDPA/WCDMA Test Signal |
| TMA | Tower Mounted Amplifiers |
| TMA | Thermal Mechanical Analysis |
| TMAH | Tetra Methyl Ammonium Hydroxide |
| TMC | Traffic Message Channel |
| TMF | Tower Mounted Filters |
| TMF | TeleManagement Forum |
| TMN | Telecommunications Management Network |
| TMO | Trans-Metro Optical |
| TMS | Test Mode Select |
| TN | Telephone Number |
| TNO | Telecommunications Network Operator |
| TO&E | Table of Organization and Equipment |
| TOD | Time Of Day |
| TOM | Telecom Operations Map |
| ToS | Type Of Service |
| TP | Twisted Pair |
| TPC | Turbo Product Codes |
| TPM | Transaction Processing Monitor |
| TPS-TC | Transmission Control Specific-Transmission Convergence |
| TQFP | Thin Quad Flat Pack semiconductor package |
| TR | Tip and Ring |
| TR | Technical Recommendation |
| TR-45 | TIA Committee-Oversees the standard making process for wireless telecommunications |
| TRA | Technology Readiness Assessment |
| TRANSEC | Transmission Security |
| TRIP | Telephony Routing Over Internet Protocol |
| TRP | Total Radiated Power |
| trTCM | Two-Rate Tri-Color Marker |
| TRx | Transceiver |
| TS | Time Series |
| TSB | Telecommunication System Bulletin |
| TSI | Time Slot Interchange |
| TSOP | Thin Small Outline Package |
| TSP | Telecommunications Service Provider |
| TSS | Telecommunications Standardization Section |
| TSSOP | Plastic Thin Shrink Small Outline Package |
| TTA | Table-Top Antenna |
| TTC | Telecommunications Technology Committee |
| TTCP | Test TCP |
| TTG | Transmit Receive Transition Gap |
| TTL | Transistor-Transistor Logic |
| TTS | Text-to-speech or TIRKS table system |
| TUI | Telephone user interface |
| TUP | Telephone User Part |
| TV | Television |
| TVSS | Tactical Video Surveilance System |
| TWG | Technical Working Group |
| TX | Transmitter |