Department of Telecommunications aka DoT has made it mandatory to use the prefix 0 will calling from a fixed-line to a mobile one. This has been in effect since the 15th of January. Those not doing so will hear an announcement when calling. This was a practice used when there was a concept called STD aka Subscriber Trunk Dialing that is outstation mobile calls. But it was withdrawn after the government allowed inter-circle mobile number portability, which meant there was no longer trunk dialing.
Knowing that India has 10-digit mobile numbers, and those starting with "0" and "1" are reserved for unique purposes, a total of approximately 800 crore numbers are possible. Traditionally Indian numbers either start with a 9 or with combinations starting with "8", and "7". We currently have a total of 115 crore numbers issued to the public. Those starting with 9 are used completely and no new number is possible. Those starting with other numbers coincide with certain numbering plans issued to landline phones. To solve the problem of avoiding confusion between the two, the prefix "0" has been re-introduced.
Currently, with these combinations a total of 115 crore mobile numbers are available. Even though the “9” series — meaning mobile numbers starting with “9” has been fully used, those starting with other numbers overlap with certain numbering plans issued to landline phones. Therefore, to create sufficient numbering combinations, the prefix “0” has been re-introduced. In addition to the subscription of mobile numbers by consumers, SIM cards are also being used for machine-to-machine communication purposes.
Apart from users, these numbers are also allotted to M2M communications. TRAI has also recommended that a 13-digit numbering system should be adopted for all SIM-based M2M connections which currently use 10- digit mobile numbers as of now, and the shift should be done as quickly as possible. This will free some more numbers to be used elsewhere.
This decision will not only clear the overlap but will also help clear the numbering resource which is already scarce. This will also help generate more than 200 crore numbers for public use in the future.