Use the code BKNOV20 to save 5% on this iPhone 4/4S All-in-One Headphone Amplifier, Extended Battery, and Protective Case that drops from the list price of 129.99 to $24.99 and then to $23.74 and get 15% off your next purchase at Sonic Electronix. Plus, the shipping is free. This is the best price we could find for this case by $16. It has a 1650mAh backup battery= and 2 headphone jacks with an amplifier designed for powering professional monitoring headphones. There is no sales tax.