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The answer is that your iPhone carrier must be AT&T, and AT&T is stretching the truth. Basically, AT&T is saying that because THEORETICALLY its 3G HSPA+ wireless network (which is what the iPhone 4S uses to connect to the internet) could someday be faster than a 4G LTE wireless networks, let's call AT&T's network 4G. Even though it is not. It is really just a fast 3G network, but 3G+ doesn't quite have the same marketing ring as 4G, so abracadabra, your iPhone suddenly says 4G.