Purchasing Japanese mobiles or buying a SIM card with the number here require the Japanese home address, however prepaid data SIM can be bought by anyone without ID nor credit card registration. Therefore, using the data SIM card is the easiest and quickest way to get cellphones brought from abroad in use without loaming. It is handy and easy recommended for someone for a short stay or for the time being.
If you are not making much phone calls, you may not need a Sim with a phone number as you can make calls using applications like whatsapp, LINE, Skype from your mobile phones.
Please note that prepaid data SIM has a validity both in duration and the data volume, you need to buy a new one to top it up once expired. If data volume gets used up before the expire date, it can still be used but slows the speed down. In order to avoid using the capacity too much is to be on Wi-Fi wherever available for steaming video or audio file, etc. there are many outside places for free WIFI access in places like Starbucks, MacDonalds or using application like Free Wi-Fi (NTTBP) that picks up the available connections nearby.
Recommended for IPhone users!
Free WiFi App