NTT DoCoMo said Wednesday it will team up with the popular social network provider Line to offer a special app for DoCoMo users, aiming to deepen its relationship with the operator of the growing communication tool.

"Line's growth has been incredible. . . . We'd like to seek many possibilities (through this partnership)," DoCoMo President Kaoru Kato said during an event in Tokyo to announce the carrier's latest handsets and services.

Since its launch in 2011, Line has gained more than 150 million users worldwide.

Through the free app, users can text message and talk to other Line users free of charge.

With the rapid growth of smartphones, people are increasingly using social-networking services to communicate with their friends and families.

DoCoMo said its Line app will be friendly for elderly users. It will also allow DoCoMo customers to easily phone each other via Line.

Line said it hopes to promote its service through the collaboration with DoCoMo, which has more than 60 million subscribers.

All of the major Japanese carriers provide their own email services, and they have been a vital communications tool for many people, especially before smartphones took off.

This is partly because instant messaging was only allowed within the same carrier until 2011.

DoCoMo has been providing an app for its email service, but it has been plagued by bugs and has not been very popular.

The carrier is now rebuilding its email service, which is expected to debut in October.

Kato said DoCoMo isn't planning to get Line to jointly develop its new email app at this point, but hinted it is a possibility in the future.