This reminded me of my earphone problems. I ended up getting a replacement pair from ebay for the price of a beer, Nokia wanted a lot more than that if I ordered it directly.

Anyway I discovered the break in mine was in the soft flexible part of the connector just above where it plugs into the phone. I could be wrong on this, but I used to wrap the cables around the phone which caused a little bend on this part of the earphone cable. So now I don't wrap the cable around the phone anymore.