Carriers around the world were no doubt aghast at the recent study finding that chat apps have overtaken traditional texting; while there's no clear leader worldwide, the likes of WhatsApp and KakaoTalk bypass contract plans and per-message costs to offer users toll-free communication across platforms. But at an NTT Docomo event today in Tokyo, Japan's largest operator announced its plans to get on board with the phenomenon. This year, Docomo will partner with chat sensation Line to provide both regular phone calls and high-quality Voice over LTE (VoLTE) communication through the app. The two companies will launch an original Android version of Line that features a dedicated call button with hooks into Docomo's network.

"The button is a kind of shortcut for making a regular call so that customers can make a regular call easily when using Line apps," a Docomo representative told The Verge. If a Line user has linked their profile and phone number, Docomo customers will have the option to initiate a call from Line itself. The carrier expects to launch the service between July and September this year.

Docomo and Line will also collaborate on an application for the operator's elderly-focused Raku Raku Smartphone series. The specialized version of Line will limit access to in-app items so that users less accustomed to smartphones avoid making accidental purchases. That app is scheduled for release toward the end of the year.

The arrangement is an undoubted coup for Docomo. While the carrier counts nearly half of Japan's population among its subscribers, its growth has been slowing in recent times as smaller rivals SoftBank and AU snap up new customers in greater numbers. Of the trio, Docomo is the only one that does not offer the iPhone, which is the most popular smartphone in Japan.

Line, on the other hand, is by some distance the most popular mobile chat client in Japan. The app borders on cultural phenomenon, with its much-aped "stickers" depicting cute bears and bunny rabbits that have grown into popular characters in their own right. Developers NHN Japan, a subsidiary of the South Korean company behind web portal Naver, announced earlier this month that Line has over 150 million users worldwide. About a third of these are in Japan.

Line has partnered with Japanese operators before, striking a deal with AU last year to include a special version of the app in its monthly Smart Pass subscription package. The new voice call partnership, however, is perhaps the most notable attempt yet by a carrier to co-opt and monetize the rise of chat apps. But it's still unclear just how successful Docomo's effort will be. CEO Kaoru Kato told reporters that calls made via the proprietary Line app will be charged at regular rates, though LTE customers will be able to call each other for free over high-quality VoLTE. With that in mind, it's hard to imagine exactly how many people might use the service — Line itself already offers basic voice chats for free, and that's not going to change with the new Docomo app.

"It is up to customers to make a regular phone call or free Line phone call," said a Docomo representative. "Some customers may prefer regular phone calls to LINE's free phone calls because of the voice quality." The demand for high quality voice calls is far from established, though, and Docomo won't make any money from its current LTE subscribers this way. It seems unlikely, too, that many users will elect to make regular calls through Line when they have the option to do the same thing for free.

Still, by partnering with a genuinely popular third-party platform, Docomo is doing more than most other carriers to embrace the proliferation of chat apps — a movement which could otherwise be seen as a threat that hijacks bandwidth while rendering lucrative services obsolete. If the gamble pays off, the carrier could see more users making traditional phone calls, while driving the adoption of VoLTE and LTE smartphones in general. But for that to happen, Docomo has to bet that its customers will change the way they've been using Line to date. And, given the chat app's meteoric success so far, that bet is far from a sure one.