I have been having the same issue over the last few months with my partners 3G... I tried all the recommended resolves but the issues continued. So I contacted Apple directly and explained the problem and its intermittent behavior... They got me to send the iPhone back and with 10 business days I received the replacement. I only had 17 days remaining warranty so I also grab the newly available iPhone extended warranty via the online store.
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15" MBP 2.4 GHz intel core 2 duo
iPhone 3GS 32GB White
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