Can Iphone bought in USA used in Singapore or Indonesia

No. Only will work at the moment in the US

Well kind of . . . only if you have an at&t account in the US. If you have US based service and took the phone over to singapore or indonesia then you should still have service, roaming service.

at&t network is GSM which is a global standard and is supported in many countries.

That's not what they wee asking though.

It can NOT be used with local coverage anywhere outside of the USA.

As of now the answer is no. But I would give time about a few weeks and I am sure the hackers will find a way of opening up the iPhone for you to do what you want. stay tuned to the major tech news sites in the US such as news.com, arstechnica.com or engadget.com.

Hence why I said, if you had an at&t account from the US, then it would work.

I was merely adding that the phone would work any where in the world that supports GSM/EDGE networks.