Make sure you clean the pin first,
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This review is from: iLuv In-Ear Tangle Free Earphones with iPhone and iPod In-line Remote with Built in Microphone - Pink (Electronics)
Bought as a present for my sister-in-law who lives on her iPhone.
At first we were very worried as she told us that sound was only coming out of one earplug. I had a quick look and discovered that the pins are covered in a light grease (probably to stop them corroding in storage). A quick wipe and voila! perfect sound.