Japan’s largest mobile operator Docomo has announced a partnership with Line, the mobile messaging app from Japan with more than 150 million registered users, that will see the two offer joint services to Docomo customers.

Under the agreement, the two companies will develop two Line-Docomo apps. One will cater for owners of the operator’s Raku-Raku smartphone range for seniors, helping older customers to better understand the service and limit their transactions and purchases of Line games and virtual goods to prevent bill shock and excessive spending.

The Raku-Raku application is slated to launch “before the end of the year”.

In addition, from September 2013, Docomo customers that use Line on an Android device will get an update that introduces a dedicated button for making voice-over-LTE (VoLTE) calls via the operator’s 4G network: Xi, which hit 10 million subscribers in February.

Docomo says the call button will allow Xi customers to call other users of the 4G network without charge, taking advantage of the quality of LTE voice calls.

Line and Docomo will also work to reduce the traffic load on the operator’s network. That’s an important measure since a number of operators have expressed their frustration with the large amounts of data that messaging apps send them. In Korea, for example, a number of operators throttled chat app Kakao Talk‘s voice call feature within a month of its launch last summer.

Docomo is Japan’s largest operator — with some 60 million customers, around 50 percent market share — but it is under pressure as the only one that doesn’t offer the iPhone. It will hope that the deal with Line is an incentive that will help keep existing users and increase the temptation for other carriers’ customer to switch over.

The deal is the second significant announcement for Docomo this week, after it invested $50 million in Pioneer on Monday. For Line, the partnership is testament to the service’s growing adoption in its home market of Japan, where it has more than 45 million users.

Indeed, such is its usage that 10 of Japan’s political parties opened ‘officials accounts’ on the service to increase their engagement with voters, following the recent reversal of legislation banning the use of the Internet in electoral campaigns.

Line’s business continues to go from strength to strength this year. The company says it is seeing increased adoption in Europe, Latin America and Africa, while it is dedicating significant resources to increasing its visibility in the US, China and Southeast Asia.

The company’s range of virtual items and its Line Game platform saw it bring in $58 million in revenue during the first quarter of 2013. With plans to introduce music and shopping services, partnerships with carriers will help not only user engagement but revenue too.

Also from the world of mobile messaging this weekMobile chat service Kakao Talk launches Facebook Home-style app in Korea, no global plans yet

Headline image via Toshifumi Kitamura / Getty Images