Keep any minimum balance in your account, so you don't have to pay a monthly fee. Pay everything through credit card, and then pay off all at once. They don't allow you to switch to another long-distance company. Instead, use a pre-paid calling card to make international calls. If you use pre-paid calling cards, it costs only 12 cents per minute to Japan.
Some phone cards are expensive.
Choose a phone card carefully. I have saved a lot of money by this method, and I really recommend this to international students. Ask a friend to cut your hair. Live within walking or biking distance to school. Residence Hall Assistantships are open to international students and provide free room and board and a small stipend.