If you’ve got money to burn and don’t mind making your iPhone quite a bit thicker, then check out the V-Moda VAMP Case for the iPhone 4/4S. The case converts digital sound to analog for a hi-fi listening experience. It’s also a headphone amp, which will allow you to use fancy headphones with your iPhone.
The one thing that you learn when you buy hi-fi headphones is that you’ll need a headphone amp for the best sound. Audiophiles rejoice, because now you can take your favorite hi-fi cans on walkabout thanks to the VAMP case. It has a 150mW × 2 amplifier that bypasses the iPhone’s internal hardware to offer improved sound. There is a volume knob, a hi/lo gain switch as well as a toggle switch with an LED indicator for Pure or VQ listening mode. There’s even an optical audio output too.
The aircraft-grade case offers 8 hours of continuous playback from its battery, which can also be used to power your iPhone when you’re running low on power. The VAMP is shipping now for a whopping $650 (USD). As ludicrous as it sounds, I wouldn’t mind listening to one with my Sennheiser HD800s, but then again, the iPhone 5 is just around the corner and if the rumors provide to be true, this case probably won’t fit on the new phone.