Reliance Jio trumpeted its 400 million customer milestone in its latest quarterly results announcement, but its net additions were actually lower than expected.

However, the Indian operator is seeing solid growth in average revenue per user and that is arguably a more important metric as it transitions from rapidly-accelerating start-up to market leader and strong digital player.

Reliance Jio reported having a total customer base of 405.6 million at the end of September, proudly declaring that it has become the first operator outside of China to cross the 400 million-subscriber mark in a single market.

It’s a headline-hitting figure, but…

Firstly, we already knew. The Telecom Regulatory Authority of India (TRAI) shared its latest market statistics earlier in October which showed that Jio passed the 400 million milestone sometime in July. Secondly, and most importantly, Jio’s growth rate in Q2 was not only lower than has become the norm but also lower than that of arch-rival Bharti Airtel.

Jio reported adding a net 7.3 million customers in Q2, which is an impressive number by most operators’ standards, but it compares unfavourably with the 24.7 million net adds it claimed in Q2 last year. To add further context, that’s less than half the net additions it announced in the same quarter three years ago.

Furthermore, Bharti Airtel’s Q2 numbers released last month showed 13.9 million net customer additions, taking its mobile customer base to 293.7 million. The once-dominant operator has posted net adds in the low-single-digit millions at best in recent quarters, with some reports showing customer losses. Clearly Bharti remains some way behind Jio in absolute terms, but it’s a sign that Jio is not having things all its own way any more.

Indeed, both operators reported monthly churn of 1.7% in Q2. That’s a significant improvement for Bharti but for Jio the opposite; the telco did not share comparative figures, but a quick trawl through its recent reports shows churn came in at 0.74% this time last year.

But while customer numbers are a closely-watched metric, there are other ways to measure the ongoing performance of a mobile operator.

Jio posted Q2 ARPU of 145 rupees (US$1.95), which equates to an increase of almost 5 rupees on the previous quarter and is up from INR127.4 in Q2 last year, or almost 14% growth year-on-year. Operating revenue came in at almost INR175 billion ($2.3 billion), up by 33% on the year-ago quarter, while the telco posted an EBITDA margin of 43.1%.

While those are healthy financials, it’s worth noting that Bharti reported a bigger increase in ARPU during the quarter, to INR162 from INR128, or a year-on-year increase of 26.6%.

It’s probably too early to start shouting about a fight-back from Bharti, but it’s one to keep an eye on.