[blimp]

i would recommend you to sign up with a proper plan, not a pre-paid. makes it cheaper to actually use.

although i wouldn't go as far as nyororin, I too stay away from softbank, since it is more difficult to calculate how much you will end up paying at the end of the month compared to the other carriers. on the other hand it is difficult to disregard from the low monthly cost of an iphone, especially if you don't call too much, or only call other softbank phone

if you want something really cheap perhaps you should look at Willcom (phs). Only time I used it was over 15 years ago so my knowledge is a bit outdated but it is said that the quality is not very good. you get what you pay for.