mobile phones in SG are not allowed to be locked.

Singtel's 3g iphones are unlocked.

In Aus, the iphone optus prepaid 16gb was going for A$849 + A$80 which is approx S$1161.25.

The iOne Plus plan total cost is S$1464.32, which is about S$303.07 more then if I purchase it in Aus and I get 24 months usage of calls + sms and warranty.

iphone warranty is only valid in the country of purchase (means if you buy it in Sg, then warranty is valid in Sg only. if you buy it in Aus, then warranty if valid in Aus only). iphone warranty is not international.