There are a few questions on this, but I couldn't quickly find any, so I don't blame you for asking ;). iFixit though, [http://www.ifixit.com/Guide/Repair/Installing-iPhone-3G-Vibrate-Ring-Switch/581/1|has a guide for fixing this switch].
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There are a few questions on this, but I couldn't quickly find any, so I don't blame you for asking ;). iFixit though, [http://www.ifixit.com/Guide/Repair/Installing-iPhone-3G-Vibrate-Ring-Switch/581/1|has a guide for fixing this switch]. The part you need to replace is the [product|IF137-004|headphone jack assembly].
There are a few questions on this, but I couldn't quickly find any, so I don't blame you for asking ;). iFixit though, [http://www.ifixit.com/Guide/Repair/Installing-iPhone-3G-Vibrate-Ring-Switch/581/1|has a guide for fixing this switch].