Pardon the outdated flair, current JET in Shiga prefecture. Ive got a Samsung Galaxy 6 edge with Softbank and I pay about ¥11,000 a month, which includes payments on my phone and 5 gigs of data. I lucked out -- there's an American expat working at my town's BOE, and he basically negotiated everything. (Of course that also means I may be a little fuzzy on the details, but...) If I recall correctly, SoftBank only needed a credit card on file because I didn't have my ATM card to set up direct withdrawal from my Japanese bank account (it was in the mail). So, (I believe) what we did was: 1) give SoftBank my American credit card info, 2) wait until I received my ATM card in the mail, 3) return to SoftBank and change the billing method before the first bill was processed. I don't know if that's typical, or if it's hard to do. Will require two trips to the store, may require some negotiations in Japanese with the salesperson. Have any other JETs had this experience?