If you have a smartphone, I would suggest putting it in "airplane mode" so that you don't incurr any of the roaming charges but can still access internet and e-mail using wifi. Then use your JA phone to call your US phone's voice mail to check messages and call people back from your JA phone. I check my US cell VM about every 3-4 days for messages when I'm there but if you need it for business, just check your Voice Mail 3-4 times a day if you have to. You can still get business done and won't have to deal with any mega cell phone bills when you get home.