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This is good news for me as I've had to turn off 3G on my iPhone 3GS to get bars. I've read how the 4S switches so I imagine that's why the option to turn off 3G isn't needed on this model. I look forward to improved signal performance with my 4S that's on it's way to my door :D
The 3GS auto switches as well, but you have the option to essentially disable auto switching by turning off 3G all together.
 
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