Hello Keito. The fact that you are using an iphone to dial out makes no difference – it’s still a phone. You can use the regular instructions we give on this site for calling the US from Japan. Basically you will add 010 to the US toll free number. For example, if the TF number is 1800 000 0000 you will dial 010 1800 000 0000. Instead of 010 you can also use the plus sign (+). One thing you should be aware of – some US toll free numbers do not work when dialed from outside the US (if the tf number’s owner chose to block these calls). And secondly, if the call goes through you will still pay international charges (it will not be a free call), this being the reason why some companies advertising a tf number block incoming international calls.