26M added on the most efficient network in the world. Open Signal testers were able to access an LTE signal 96.4% of the time. That's more than comparable testing on any of the U.S. carriers. Jio pledges to reach 99% of the 1.3B Indians by the end of 2018.
The secret sauce is a state of the art all-IP 4G network that delivers data for ~$0.05 per marginal gigabit. The network cost > $20B to build, but once in place has very low marginal costs. The 150,000 base stations are two or three times as many as Verizon or AT&T, many with Massive MIMO.
They control 300,000 kilometers of domestic fiber and a share of 25,000 kilometers of undersea international.