Russian website Mobile-Review has been looking into the Nokia 5800’s earpiece woes and has produced a lengthy account of its investigation and the subsequent conclusion. They even have an official statement from Nokia.

They used multiple 5800’s in different settings and have come up with the following:

• How long the phone is going to work before its earpiece breaks down depends on various factors and has nothing to do with the defect of the top right corner of the casing;
• All broken earpieces have knobby contact surfaces (we examined them with an electron microscope) as well as scuffs all over juncture points;
• As a rule the 5800’s earpiece works for at least a month before giving up the ghost.

The key conclusion being:

• The failure occurred only when a working phone was placed in the box with the above mentioned air humidity level, our reference sample that spent two weeks in the same box, but was turned off, didn’t show any signs of this problem.

Basically, the earpieces were faulty and Nokia changed its earpiece suppliers in late January so therefore 5800s made (not bought) February 2009 onwards should be just fine. If you have a 5800 made before then, it is probable that you have a faulty earpiece. The simple solution to this problem is to hand over your 5800 to the Nokia Service Center and get the earpiece replaced.