My experience is that it is worse then my tilt. Where I get good service inside my house with the iPhone it goes from 1 bar to 3. The tilt goes from 3 to 4. It sometimes loses 3G while tilt never did. Other places where I have 1 bar with the tilt I could still make phone calls. The iPhone in the same are I get call fails and drops. Where the coverage is strong they are both strong it is when it comes to areas that the signal is weaker that the iPhone has a problem for me.

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iPhone 3G 2.0.2 Jailbroken
tilt WM 6.1 L26 KaiserDiamond v12 Throttle Launch