V-Moda came out with a amp/DAC case for the iPhone although it was very pricy, but with the release of the Vamp Verza and the capability to use it for iPhone, Android and Windows phones, makes this product revolutionary. The Vamp Verza is a combination of both a digital-to-analog signal converter and a headphone amplifier. The Vamp Verza will turn the 0 and 1's in your music files into analog signals thus making the quality of your sound increasingly better.
The Vamp Verza will be designed for the most popular iPhone and Android phones as well as most tables. Currently the Vamp Verza comes in cases specifically for the iPhone 4/S and the Samsung Galaxy SIII, although more are in design.
The Vamp Verza will cost $600 and each specifically designed case for the phone will cost an additional $100. If you're serious about your sound, than this is something you may want to consider.
For more information on the Vamp Verza, click here.