Ok, so before I start buying stuff I guess I should ask this. Does the hub have to be an externally powered hub, or can it be a buss powered hub assuming that only the amp and the phone are connected to it. Also, is the phone going to drain the batteries in the hub to charge the phone battery, lol that would be annoying.
I looked it up and usb ports put out 5 volts. So 4 AAA batteries would probably be the best fit, at 6 volts to power a buss powered hub. I found this one which is nice and small. http://www.google.com/products/catalog?hl=en&q=2+port+powered+usb+hub&gs_upl=1075669l1084447l5l1084888l22l18l0l3l3l1l317l3272l0.10.7.1l21l0&bav=on.2,or.r_gc.r_pw.,cf.osb&biw=1280&bih=851&um=1&ie=UTF-8&tbm=shop&cid=3294761403035180482&sa=X&ei=6Tf9TuTyJrDZiQLT3PzCDg&ved=0CH8Q8wIwAA.
Assuming this would work, and assuming that you wouldn't burn through batteries quicker then **** while unintentionally charging your cellphone. We should be able to get a compact cube shaped chassis from radio shack for the batteries. We could just cut the usb cord from the hub nice and short, and splice the power lines from the striped usb cable to the battery pack, and then glue it together. Then we would preferably have a very short usb to mini usb cable, and a short USB to micro USB cable, depending on the phone.
So how much would this device cost? The hub is like 6 bucks, 4 or 5 for batteries, probably 5 bucks for the battery pack, and then another 10 bucks for cables if you don't want a mess of USB cabling in your pocket. So 26 bucks.
On further thought, you might be able to do this using a lithium ion battery. Then check it. You buy a charger pad, and you drop the whole bundle, phone, amp-dac(if you have an e7), and USB hub onto the pad and it's all getting charged. Also if I'm right that the phone will drain the USB battery, this would essentially give you double the battery life on your phone.
This all seems pretty ghetto, but I'm getting excited, this might actually work and be functional.
Common guys, get online and tell me what you think.