The telecommunication technology in India has really come out of age and the state of Tamil Nadu is no exception to this development. Tamil Nadu is among the technologically advanced states of India and thus it has been able to reach almost every parts of the state by telephones. These regions are well divided by the system of Telephone Code. The telephone codes has come a great help in the telephonic demarcations of the state. Some of the areas have five digit telephone numbers, while others have six to seven digit preceded by the Subscriber Trunk Dialling or S.T.D. Codes.
The Tamil Nadu Telecom Circle provides a good service throughout the state and offers facilities like basic telephones, ISDN, Internet, leased line and I-net. Apart from these, they also provide the cellular service. The use of telephones in Tamil Nadu is increasing day by day and the growing number of telephone connections prove the point. Even the villages are no alien to this fact and most of the villages in the state are under the telecommunication system. Telephone Codes of some of the main cities and towns of the state are given below:
| Cities | STD Codes |
| Chennai | 044 |
| Coimbatore | 0422 |
| Cuddalore | 04142 |
| Dharmapuri | 04342 |
| Dindigul | 0451 |
| Erode | 0424 |
| Kancheepuram | 04112 |
| Nagercoil | 04652 |
| Karur | 04324 |
| Krishnagiri | 04343 |
| Madurai | 0452 |
| Nagappattinam | 04365 |
| Namakkal | 04286 |
| Udhagamandalam | Not Available |
| Perambalur | 04328 |
| Pudukkottai | 04322 |
| Ramanathapuram | 04567 |
| Salem | 0427 |
| Sivagangai | 04575 |
| Thanjavur | 04362 |
| Theni | 04546 |
| Thiruvallur | Not Available |
| Thoothukudi | Not Available |
| Tiruchirapalli | Not Available |
| Tirunelveli | 0462 |
| Tiruvannamalai | 04175 |
| Vellore | 0416 |
| Villupuram | 04146 |
| Virudhunagar | 04562 |
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