Roaming service enables you to use your own mobile phone, with the same telephone number used at home, via SoftBank network. Be sure to confirm that your mobile would work in Japan before your departure.
Check if your network provider is listed in below, you are able to use roaming service in SoftBank.
Use W-CDMA (3G) 2100 Mhz network compatible handsets.
You may need a prior enrollment with your own mobile network operator to roam in Japan. Check your subscription status and make the necessary arrangements.
For those without a W-CDMA (3G) handset, SoftBank offers handset rentals. Make your rental reservation before your arriving in Japan.