I somewhat doubt that it would work here in the US as Japan uses different frequencies than we do here in the US.
Might try horizonwirelessonline to get an unlock code. They are one of our forum sponsors and come highly recommended.
It shouldn't matter that it is an NTT PIN. All you need are to have the device properly provisioned for service by ATT, service books sent and received and then log into BIS and enter the IMEI and PIN.
As long as you have a BB data plan, it should work, provided the unlock works and the freqs are the same.