The number of users on Zalo, a mobile-based free texting and calling app, is now equal to half of Vietnam’s population and matches the number of subscribers of the country’s biggest mobile carrier.

The operator of the app announced it had reached a new milestone of 45 million users on Wednesday, a significant expansion from one million users in March 2013.

According to tech website ICTnews, the number of Zalo users matches that of the military-run Viettel, Vietnam’s largest mobile network operator.

Vietnam’s population reached 90 million in November 2013.

A product of Vietnam’s tech giant VNG Corp., Zalo allows users to send text messages and make phone calls free-of-charge via the Internet. Users can also open a Zalo profile to connect with friends online, similar to Facebook.

It is considered Vietnam’s leading over-the-top (OTT) app, beating out strong foreign competitors such as Viber, Line, and the Facebook-owned Whatsapp in the local market.

OTT refers to delivery of audio, video and other media over the Internet without the involvement of a multiple-system operator in the control or distribution of content. People can use OTT apps to communicate without having to pay for charges as they do with traditional mobile communications.

Zalo was launched in late 2012 and reached 30 million users in May 2015, growing by 10 million users compared to the preceding six months.

In July of the same year, Viber announced the closing of its Vietnam office, enabling Zalo to dominate the market.

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