american iphone with a japanese plan?

I can't explain the whole situation so if I say "there is no other option," please believe me.

background information:
currently, I am living in america but next year I will move to japan for a couple of years (yay!). right now, I am on the same crappy cell phone plan with my mom and sister. my mom is wanting to get a better phone plan immediately for business reasons. this means that we all need to buy new phones. I wasn't really interested in getting a new phone because I will leave soon so it won't matter. but here's the catch: my mom doesn't know about my plans to move to japan. like I said, I'm not explaining it but I can't tell her about it. just trust me, telling her is not an option so please don't waste your time suggesting it.

summary:
I'm moving to japan soon, but I pretty much have no choice but to buy a new phone in america like right now.

the actual question:
if I bought something like an Iphone (a phone that is used in america and japan), could i buy it in america (it would be unlocked of course, so not tied to any specific american company like verizon)and then take it to japan and get a cell phone plan with a japanese company?

short version:
can I use an unlocked Iphone from america with a japanese cell phone plan?

sorry to write so much. I would appreciate any advice you have about japanese cell phone companies. thanks!

if I bought something like an Iphone (a phone that is used in america and japan), could i buy it in america (it would be unlocked of course, so not tied to any specific american company like verizon)and then take it to japan and get a cell phone plan with a japanese company?

Yes, it is possible, but it will be expensive for your mother both upfront (unlocked phones are often considerably more expensive and convincing her to get you one will require some explaining), and in cancellation fees when you eventually drop your service. Also, you will be fairly restricted in your options on the Japanese end, with B-mobile as one of the few companies that you'll be able to contract with for a reasonable price.

If you're positive you'll be moving to Japan in the next year then it would be prudent to get a cheap phone for the time being and then get a contract for a new phone once in Japan. Some phones, like the iphone, are significantly cheaper in Japan than in the US.