Subscriber trunk dialling 
(STD) codes are assigned to each city, town and village. These codes
can be between 2 and 8 digits long, with the largest metropolitan areas and cities having the
shortest (two-digit) codes:
   11 - New Delhi, Delhi
   22 - Mumbai, Maharashtra
   33 - Kolkata, West Bengal
   44 - Chennai, Tamil Nadu
   20 - Pune, Maharashtra
   40 - Hyderabad, Telangana
   79 - Ahmedabad, Gujarat
   80 - Bengaluru, Karnataka
Second-tier cities and metropolitan areas, as well as large or particularly significant towns have
three-digit area codes:
   120 - Ghaziabad and Noida, Uttar Pradesh
   124 - Gurugram, Haryana
   129 - Faridabad, Haryana
   135 - Dehradun, Uttarakhand
   141 - Jaipur, Rajasthan
   160 - Kharar, Punjab
   161 - Ludhiana, Punjab
   172 - Chandigarh Capital Region, Chandigarh[1]
   175 - Patiala, Punjab
   181 - Jalandhar, Punjab
   183 - Amritsar, Punjab
   233 - Sangli, Maharashtra
   240 - Aurangabad, Maharashtra
   241 - Ahmednagar, Maharashtra
   250 - Vasai-Virar, Maharashtra
   251 - Kalyan-Dombivli, Maharashtra
   253 - Nashik, Maharashtra
   257 - Jalgaon, Maharashtra
   260 - Daman, Dadra and Nagar Haveli and Daman and Diu
   261 - Surat, Gujarat
   265 - Vadodara, Gujarat
   343 - Durgapur, West Bengal
   413 - Puducherry, Puducherry
   422 - Coimbatore, Tamil Nadu
   431 - Tiruchirappalli, Tamil Nadu
   452 - Madurai, Tamil Nadu
   462 - Tirunelveli, Tamil Nadu
   471 - Thiruvananthapuram, Kerala
   474 - Kollam, Kerala
   484 - Kochi, Kerala
   512 - Kanpur, Uttar Pradesh
   522 - Lucknow, Uttar Pradesh
   532 - Allahabad, Uttar Pradesh
   542 - Varanasi, Uttar Pradesh
   551 - Gorakhpur, Uttar Pradesh
   562 - Agra, Uttar Pradesh
   581 - Bareilly, Uttar Pradesh
   591 - Moradabad, Uttar Pradesh
   621 - Muzaffarpur, Bihar
   612 - Patna, Bihar
   641 - Bhagalpur, Bihar
   657 - Jamshedpur, Jharkhand
   712 - Nagpur, Maharashtra
   721 - Amravati, Maharashtra
   724 - Akola, Maharashtra
   751 - Gwalior, Madhya Pradesh
   761 - Jabalpur, Madhya Pradesh
   821 - Mysore, Karnataka
   831 - Belgaum, Karnataka
   836 - Hubli-Dharwad, Karnataka
   870 - Warangal, Telangana
   891 - Visakhapatnam, Andhra Pradesh
The first-ever long-distance subscriber trunk dialling (STD) call in India was made between the
cities of Kanpur and Lucknow in 1960.[citation needed]
The total length of all phone numbers (area code and the phone number) is constant at 10 digits.
For example, the number 7513200000 signifies the area code 751 (the area code for Gwalior)
followed by the phone number.
Fixed-line or landline numbers are at most 8 digits long.
Fixed-line operators
Due to the availability of multiple operators offering fixed-line (landline) services (either wired or
wireless), there is an operator code for each telephone number, which is the first digit in the
phone number.[2][3]
          Operator             Prefix
 BSNL / MTNL                   2
 Reliance
                               3
 Communications
 Airtel                        4
 MTS / HFCL                    5
 Tata Indicom                  6
 Datacom Solutions             7