I just got off the phone with Griffin customer support and have been informed that Griffin is in the process of "inventing" and clearboost case for the iPhone 3G to help improve signal quality for both 3G network and edge network.
It is not available as of this moment, but thought since I got an insider's word I would share with the best iPhone web site on the internet.
I saw a picture of it before.. there is a wide antenna sticking out from the middle top..
(edit)
This was for the original iPhone:
Reviews for it said it was a nice case but didn't boost the signal at all..
That is butt-fuggin ugly!
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