Here is a great tool to identify that which Mobile series is of which operator (Mobile Co.)
Just enter four digit series no. and it will tell you the operator name with state.(This has for Indian Operators Only)
not only this you can know the country name by ISD code, to know this enter ISD code and you will get the country name of the relative code.
Here is Screenshot
You can get it here
INDIADAWN - World Of Happiness - View topic - Mobile Series Identifier For Mobile