Messaging Apps in Japan

Hi there,
Quite a few threads have discussed prepaid SIM cards in Japan, but I cannot seem to find a specific answer to my questions. While currently staying in Japan for several months, I would like to buy a prepaid SIM card just for data, which seems to be the cheapest option. In addition, I would really like to continue using WhatsApp because it's the main messaging app for friends and family back home. This includes some people who will come to visit me here, people I would like to contact while they are also in Japan, at any time of the day.

These SIM cards come without a phone number but the people in this forum seemed to be able to use WhatsApp regardless. It may be a very technical question, but is it possible to use WhatsApp after all with these Japanese SIM cards? If it isn't possible, is there an easy alternative (perhaps not Line) which my friends from back home and me could easily use (no voice apps)?

Thank you for any help, it is highly appreciated!

I can't comment on which sim to purchase in Japan, I get mine from my home country, it's cheaper for me, As for whatapps, if it's already setup, regardless of what sim you use it will still work as long as you have a wifi or data connection.

WhatsApp will still work as long as you don't restart the mobile unit and the account is already signed in. The better option is to not get a data SIM, just rent a WiMax from the airport. This provides unlimited data, then connect to it as WiFi, turn off the cellular on your mobile and it will work fine.

I bought a sim card from B-Mobile and picked it up at the airport post office. WhatsApp worked fine, as usual, even though it didn't sound like it would from what I'd read online!

Do you and your friends use Facebook? Facebook Messenger is another thing you could use, and I would assume most of you already have accounts on!

I think there is no restriction toward a specific application in Japan. it is not China.
data SIM connects you to internet which has no restriction in Japan.
generally speaking, those applications request that you use the same account in one instrument (one sim). you have to take a necessary procedure to transfer the account from sim A to sim B. if you fail to do that, you will lose the data.

Thanks everyone, this is very helpful! I didn't know WhatsApp can stay logged in between changing SIM cards, which will be worth a try. Based on everything I read online I have been skeptical as well about this working out. I'm keeping my fingers crossed that saving WhatsApp pictures on my phone will make the transfer smoothly (as if there were no transfer, hopefully).

Thanks again everyone!

As long as you dont delete whatsapp from your smartphone, you can continue to use it, even if you have no sim, it will still work, this goes for wechat, line and many other messaging apps, as long as you connected online, you are good to go.