Thanks a lot of all the advice, gang! Yea, SoftBank sure makes things complicated, lol.
I think I'll start off with the White plan and the data plan that's NOT "unlimited," figuring that I can always call them and upgrade to a bigger plan if I need it--typically companies are fine with you deciding to give them more money
Is it better to just buy the iPhone 4 outright or to pay in monthly installments? Typically places charge MORE for the monthly payment plans. I'll be in Misawa for at least 3 years, so paying it off in time is not an issue, though, if the monthly plan isn't any more expensive.
I think of it as more choice, not complicated.
First off, are you really, really sure you won't be going over 8.7MB a month? Remember, even if you view a YouTube video, you could be hitting the limit straight away.
Next, changing plans. You should find out if Softbank will actually let you do this. Strange that they shouldn't, I know, but then Japan has been know for some strange stuff. Ever heard the story about the guy who went into McDonalds in Japan and asked for a burger without pickles? He was told he had to have pickles as they were part of the burger.
And if they do let you change plans midway though, see if they will charge you an administration fee. I can't remember what it is. Something like 2000 Yen plus tax. I know they charge you this when you upgrade to a new phone. Also, they may insist that you pay a fee for changing/breaking the original contract, and insist that you start the contract period afresh - meaning 24/25 months from that point on.
If you're going to be here for more than two years, it'll be cheaper to sign up than to buy the phone. Actually, I spoke to a guy at Yodobashi about six months ago, and he said that Softbank do not allow the sales of handsets any more. They all have to be on contract.
I don't know if it's possible or if it'll work out cheaper, but maybe you can get an iPhone from abroad, and put a Softbank SIM in it. If you really don't want the data plan, you could get around the contract and just end up paying for White Plan plus the email plan.
And don't forget, being Softbank, it'll more than likely be SIM locked if you get it here. Useless if you take it abroad when you leave Japan, unless they find a way to, ahem, get around it, in the future.