The Street is claiming that the reason Apple has delayed the white iPhone 4 until "later this year" is due to light leaking around the edges of the glass. This according to the ever popular "person familiar with", in this case the manufacturing process.
As the source described it, if it were a metal or plastic material, a simple coating would fill in the gaps and block the internal light. Glass is an entirely different issue.
Take this with a white iPhone 4-sized grain of salt, of course.