In Japan, people usually use the regular mail or LINE for communicating.
In India too there are frequently used messaging tools, but they are not the same as the ones used in Japan.
In India, SMS or Whatsapp are the frequently used.
SMS are messages sent directly through telephone lines and Whatsapp is a smart phone application like LINE.
As SMS is sent through telephone lines, telephone charges are applicable; while for sending messages through Whatsapp only internet charges are applicable, just like LINE.
If you opt for unlimited internet plan, you will not have to pay extra internet charges for using Whatsapp.
In India, smart phone are widely used, but many people still use traditional flip phones (like the Japanese ガラケーphones).
Whatsapp cannot be used on these normal phones; hence people not having smart phones use SMS for messaging.
When you are in India, make sure you download Whatsapp.
Whatsapp is widely used outside Japan.
In Japan, LINE is usually used but in other countries, it seems that very few people use it.
When you make Indian friends, they ask you if you use Whatsapp.
If you exchange mobile numbers with someone, or if you make a call to them once and they have Whatsapp installed in their phones, they automatically get added to your Whatsapp friends.
Whatsapp is very useful to make new friends and expand your network of contacts.
Usually Indians do not reply to e-mails promptly, but if you message them on Whatsapp or SMS, they reply quite instantly.
Even if you leave India, you can keep in touch with your friends through internet.
Also, ‘We Chat’ is also used by many people in India, but there are also a lot of people who do not use it.
It should be sufficient to have only Whatsapp.
So before going to India, please make sure you download Whatsapp in your Phone!