except for the 3G PRS-900 can be used anywhere. The problem maybe to get one as it's only sold in the U.S. But you may use usunlocked.com to buy directly at SonyStyle.com and get it shipped to singapure. You may have already seen some threads about PRS-900, features and uslocked here.
I live in Germany and bought one through eBay. It works fine except for 3G but that's ok for me.