line app

Is the line app for phones really useful and what are the benefits of it?

It works just like skype, viber, etc. but seems to be more popular here than those other apps so there is a better chance that your friends will be on line than on anything else. The benefits are free calling to other line app members which can really cut down on calling costs for smartphone users in Japan since we don't typically get free minutes included in our plans.

Line is rather for messaging than calling. In Japan you can't text a friend unless he or she is at the same mobile netowork (so for example I can text my friends who have softbank mobiles, but I can't those who have docomo).
So you need to use e-mails that are very inconvenient. Line lets you to text everybody for free and even to send some cute stickers, make groups, play games, etc.

People in Japan also like to text each other on Line instead of using emails too if they want to have a more immediate conversation. They also like sending the stickers to each other. And some of the Line sticker characters are so popular you will see them as phone straps, real stickers or various other things.

In Japan you can't text a friend unless he or she is at the same mobile netowork (so for example I can text my friends who have softbank mobiles, but I can't those who have docomo).

It used to be the case where you couldn't sent out of network sms but that is no longer the situation. Japanese phones can now sms each other regardless of network.

But it doesn't really matter because no one really uses sms anyway as the superior MMS system is used instead.

So you need to use e-mails that are very inconvenient.

It depends on your phone, but most smartphones treats sms/mms like chat conversations so there is almost no difference between using regular messaging and line.

Lots of people use LINE for voice calls also.