If you are a SoftBank customer who wants to upgrade to iPhone, here is the price you will have to pay for the pleasure:
Discounted with the new super bonus:
8GB model 30240Yen - monthly 1260Yen
16GB model 41760Yen - monthly 1740Yen
Compared to MNP and "New Contract" price, both 8GB and 16GB will cost 300Yen more per month. Keep in mind that all of the current "New Super Bonus" customers will need to payback remaining installments (not discounted!) for their phones. One can check remaining payments on the My SoftBank website.
This information came to us directly from one of the SoftBank's store managers.