When was the compact cube charger introduced for the iPhone? Does anyone know when the compact cube charger was introduced for the iPhone? 

I am looking for an official source, either from Apple's website or an industry magazine / web article.

It was 2008 at the latest; I did find an Apple webpage on the 2008 recall of the AC mains prongs coming loose.
The cube charger was released with the iPhone 3G on July 11, 2008. A review of the 3G mentions it:


  The plug is pleasantly smaller than on the original iPhone's, but it's compatible with a standard USB cable.