If you are staying in India, either temporarily or permanently, you might get cell phone calls from numbers you don't recognize. Although all mobile numbers in India are registered, not all numbers are listed. Still, you can at least find out what state the number is registered in.
Check the first two numbers in the phone number. The first of these will be 7, 8 or 9. This number tells you how old the number is (the newest series of numbers begins with a 9). The second number combined with the first tells you which mobile operator the phone is registered to.
Check the next two numbers in the phone number and refer to the numbering plan on India's Department of Communications website. Combined with the first two numbers, they will tell you which state the mobile phone is registered in. For example, if the number is 9016, the number will be registered in Gujarat with the Reliance Communications service provider.
Check the remaining six numbers with the mobile phone operator it is registered to. Often this step involves calling the mobile operator in question. You might be able to get the individual or enterprise the number is listed to. Not all phone numbers are public, however, so this step might prove inconclusive.