From my knowledge, you CANNOT buy unlocked 903sh in Tokyo. Sharp only makes 903sh for Vodafone and it is incompatible with other carriers in Japan such as AU/KDDI, DoCoMo etc. Therefore there is no such thing as unlocked phone.
What you are looking for is a de-commissioned phone - meaning the phone is been released from Vodafone's service contract. (Either the contract term has expired or pre-maturely terminated ). What people in Taiwan usually do is buy the 903sh from stores like Bic Camera or Sakura-ya, break contract the next day, pay the fine for pre-mature contract termination, bring the phone back to Taiwan and flash the phone with a "custom" firmware that "unlocks" the phone to recognize USIM cards other than Vodafone's.
To this day, there is no PERFECT custom firmware. All versions out there are flawed in some aspect such as loss of Java, no MP3 player, GPRS, WAP and random malfunction.(Just take a look at SHARP discussion board)
Something you might want to consider before taking the plunge.
To everyone out there: iIf my information is incorrect, please correct as necessary.