Gonna study in Japan -- can I use my iPhone?

I've read dozens of threads and various articles, and from what I've gathered so far (correct me if I'm wrong):

1. Unlocked iPhones can be used in Japan, but unless I use MVNO, they're practically useless as the 3 biggest carriers won't give me a sim once they find out my IMEI isn't under their Japanese phones list since it means the shutter sound can be muted.

2. MVNO is pretty reliable but very slow speed, and requires credit card (which I don't have).

3. If I buy an iPhone in Japan, I can get it unlocked, due to the recent regulation that obligates carriers to unlock customers' phones upon request, be it after the 2 year contract ends or not.

Can anyone recommend me whether to use my unlocked iPhone, or just buy a new one? Hopefully I'm gonna stay for more than 2 years, so using rental phones is obviously not an option.

Buy the lowest spec phone/SIM package from Softabank or DoCoMo. Swap the SIM later.