From January 15, all landline phones dialling mobile numbers will need to prefix “0” first, the Department of Telecommunications ordered on November 20 and November 26. In 2012, the DoT had expressed some scepticism on the idea, but seems to have reversed course, seeing how ten-digit numbering seems to have a ceiling. As tens of millions of people migrate to other subscribers (and not all bothering with mobile number portability that lets them keep their old number), and many people owning multiple SIMs, ten-digit numbering might cause issues if billions of mobile-connected IoT devices start to proliferate. Requiring a zero to be input before ten digit mobile numbering systems essentially gives the numbering system room to add ten times as many subscribers.
TRAI had recommended this move in May. On top of a long-term availability of upwards of 10 billion numbers, there was a much more pressing near-term concern. More and more mobile numbers are beginning with 8, 7, and 6, due to the increase in demand for new numbers driven by, among other things, the entry of Reliance Jio. As such, there’s a risk that landline numbers starting with some of the first few integers of newer mobile number ranges will thwart attempts to call newer mobile numbers. Requiring zero in front of mobile numbers solves that issue, as it lets landline call providers clearly distinguish between attempts to call mobile and landline numbers — landline numbers are shorter and networks tend to immediately call such numbers when the number of digits dialled reaches a certain threshold.
The DoT said in its order that in the interceding period between now and January 15, landline providers must play back a message informing users that starting January 15, dialling mobile numbers will require a zero.