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					Originally Posted by  S-Man
					 
				 
				Disposable prepaid SIM cards should provide some anonymity until folks are required to register them. 
			
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Nope, this won't work with a stock iPhone 4.  To activate an iPhone 4 in this country, you must assign it to an AT&T account.  Once you do that, it's locked to the AT&T account and won't work with a prepaid SIM.  Not only that, the iPhone 4 uses the micro-sim format, which is not supported by all of the prepaid options.
Yes, you can (easily) jailbreak your iPhone 4 and, if you do, you can unlock it AND use Facetime over 3G.  However, most people are too lazy or too worried about voiding their warranty to go this route.