Apple hand-held products

I'm currently interested in this piece of information:

http://www.everyipod.com/iphone-faq/ipho...phone.html

For those interested in buying an unlocked iPhone, it is strongly recommended that one buy from an authorized reseller outside of the US, preferably in person, to avoid potential issues in the future related to unofficial unlocking methods. Theoretically, unofficial "hack" methods could compromise data security and Apple or a carrier could remotely disable the device entirely as well.

Americans should note that the world is full of beautiful countries that do not lock the iPhone to a carrier from Belgium to the Czech Republic, Hong Kong to New Zealand, along with many others, so consider picking up an iPhone while on vacation. Naturally, be sure to verify that the iPhone 4 is for sale in the country of interest and has officially unlocked models in stock prior to departure. Bon voyage!

And I happened to check out this page: http://support.apple.com/kb/HT1937
to see that my country, Vietnam, is on the list.

What exactly does this mean? If I buy one from over here, will it be legally unlocked by Apple itself to allow uses of local (Vietnamese) network providers? Will it be fully functional in American boundaries should I ship it over, using an American cellphone service provider such as T-Mobile?
I'll take care of small details such as national electricity voltage and such later, right now I'm focusing on avoiding AT&T contract.

Also, for clarity's sake:
- SIM unlocking = allowing use of different cellphone carriers
- Jailbreaking = allowing use of various applications

Yes/No?