Is it cheaper to buy Apple products from the USA?

Will be going to USA soon and was wondering if it was cheaper to buy an iphone there versus buying it in SG. Noted that you have no warranty, need to pay taxes at Changi on return. After factoring in the additional 7%, possible it is still cheaper to buy in the USA? And... if u buy it, open it and use it right away there and then, u probably need not declare at customs right? So there a tax savings of 7% (assuming prices in SG and USA are the same)