In my country, quite a number of vendors are selling the "so-called" unlocked phones which came from Singapore, HK, NZ etc.
At times, some vendor claimed their USA iPhone 3G is actually unlocked and surprisingly some people have tested and it works (without any turbosim etc)!

Is there a way to verify for which operator the iPhone 3G is meant for when this vendor supply it to the market?
Is it through the "Model" number such as shown here --> http://support.apple.com/kb/HT1937

Sometimes the box don't have the similar Serial, IMEI number as the iPhone 3G inside... Thus, we need to check the Settings/General/About to know the info.

Can anyone advice? Thanks..

Well, I guess the serial no. must be having the info. but I dont think the number position and country is discovered by anyone yet.... Maybe, the 3rd and 4th position would be the country code or something.....

If you can get hold of an iPhone 3G of a friend, you can ask him the country it is for and try to find the country code in the serial no.....

Thanks for the reply but I tried to google and see if serial number can reveal anything but found none.

I have looked at two iPhone 3G's model part number and as stated in the site here --> http://support.apple.com/kb/HT1937

The Model numbers seems to be are AT&T. One which is confirmed locked but the other one seems to be "unlocked"...hmmm I just wonder why?

Edoras

I have been duped myself. I just bought an iPhone 3G which they claimed was an officially unlocked piece from HongKong. I came home and blogged through this gem of a forum and found out that there is a XSim soldered to my iPhone-3G.

So at first what seems like a perfectly normal iPhone-3G with the Sim tray perfectly normal there is a XSim soldered inside your phone.

To check this (as suggested by Mr. Bob and others)

1) Turn your phone to airplane mode and then toggle it back on!!

2) There would be no "carrier" option in the Settings menu

3) The GPRS or Edge symbol would go away after sometime and to get it back you have to reboot the phone.

If you have all of these problems in the so called unlocked phone. It means your iphone-3g is AT&T iphone which has been hardware modded.

Thanks niks77 - This confirmed my suspicion...!