Hmmm isnt it more efficient and cost saving to just get those data sim card from japan airport if thats the case? Not too sure as i haven been to japan before. Thanks!
the most cost efficient IMO is the starhub happyroam now. The benefits are many fold
1)Ready to use upon touch down as the sim is set up in SIN
2)while u are in SIN, you still have access to data meaning your whatsapp etc still works as per normal
3)unfinished data still can be used while u are back in SIN, assuming your subscribed period is still not due. If say u turn on data plan from 1 April, and you return from JP on 15 Apr, and on 20 April u go to JB for some seafood, both your JP and JB is still able to use the same data plan, assuming you have left over and paid for a 30 days plan.
4)Happyroam JP use 2 big JP networks, namely Docomo and KDDI. Theoretically better than the JP local sim as they are all riding on one network, most of them Docomo's.
$15 for 2.4GB 30days are a steal.
Disclaimer: I am not working for Starhub or have any business relationship with them.