This one looks very interesting:
http://www.myjapanphone.com/latest_promotion.htm
Look at "Japan Cell Phone Rental" down the page under the Fuji promo.

1st week FREE rental but you must use the $30 in long distance airtime,
which will be no problem.  Call USA for UNDER a dollar a minute!  Hell,
that beats Verizon calling Japan by 40%!  $.70/min Japan calls.

And here's the kicker I liked:
ALL INCOMING CALLS ARE FREE FROM ANYWHERE!  If YOU call THEM in Japan, they
pay NO AIRTIME!

only $2/day after the free week.....which is also dirt cheap from the
others I looked at....$14/week.

Get it before you leave, return it when you get back to the USA, no
searching for it in a strange city with millions of people....another real
feature unless you're from Osaka...(c;

Look around for the best VoIP calling rates to Japan mobiles, some as cheap
as a couple of pennies per minute from your PC...and the person on the
rental phone in Japan above pays nothing extra!