well cant you use the iphone in a supported country just by putting in the supported carrier i heard with a bit of hacking you can use it without unlocking am i wrong or right? Because i just got the iphone 3g and its awesome but i want to use it in europe on christmas and i want it unlocked damn you at&t
If you bought an iPhone from AT&T, then that iPhone will
only accept AT&T-branded SIM cards. If you want to circumvent that and use a SIM card from a different carrier, you'd need to unlock it. AT&T will not help you do this, and if you go through a 3rd party to do it, you'll lose your warranty. I honestly don't know for sure (I've read conflicting reports about it) whether or not any 3rd party actually knows how to unlock the 3G iPhone yet.
The very first officially unlocked phones in France were crippled by a bug in firmware version 1.1.2. That bug was fixed in 1.1.3, and they now work internationally.
I'd expect that if you purchase a contract-free (prepaid, Pay As You Go, or whatever other trademark your carrier uses for the concept) iPhone from a carrier that offers an unlocked option, then you'd stand the best chance of having a hassle-free in-store experience with no long-standing contract issues once you get back home. You should expect to pay significantly extra up-front for the hardware if you go down that route, though.
Also, keep in mind that in France, at least for the first generation iPhone, the act of unlocking the iPhone was separate and not dependent upon the act of getting it without a contract. The contract-free iPhone had a certain price premium attached to it, but it was still locked in to only accept SIM cards from Orange's network.
Then, regardless of whether you opted for the contract version or the no-contract version, after six months from the date of purchase, you could request to have the SIM lock removed for free. If you wanted to remove the SIM lock earlier than that, you had to pay another extra fee.