How much does it cost for a new IPhone 4 battery?

My IPhone 4 was working perfectly fine a few weeks ago, and then the next day, it stopped charging. My IPhone had eventually died, and now that it had ran completely down, it won't charge, and it won't even show that thing when you try to open your phone and it tells you you need connect it to the charger because your phone is dead. I think my battery just burned out, I've had my phone since Christmas 2011, and it happened in the end of March. How much does it cost to get my battery replaced?

Help MY TWITTER IS STUCK ON PRIVATE?

Somehow i made my twitter private and i can't unprivate it. I've tried everything on settings. And when i research it everything says to go to some checklist… WHAT CHECKLIST. I should mention that i have an iphone and an ipad so if it only works on a computer or something please let me know.oh and the question is how do i take it off of private?

How to internally customize my iPhone 5?

I have an iPhone 5 and I have heard there are websites where you send in your phone and they put better parts or gadgets in your phone what are some of these websites please!

IPhone music album artwork gone?

I plugged my iPhone 4 into my laptop and went to iTunes to put music from my laptop to my phone. Not all of it is missing but most of it that I bought from iTunes is gone. The music that I transferred had album artwork. How can I get the album artwork back onto my phone?

My roommates iphone is locked?

Ok so she can't remember the password and i'm trying to back it up on itunes on my laptop but its not working because itunes is not letting me and it keeps saying to try to put the password in again but we can't remember.

Where is the MAC address on my iPhone 4S?

I need to know the MAC address to put down on a waiver form so I can use my phone in class and I have no idea what it is or where I can find it. Someone help me out?

If i buy an iphone off of amazon, can i use that on my at&t carrier?

I do not really know how to word it, but long story short i broke my phone. I have at&t but since my broken phone is older, they don't carry them in the store anymore. So not really thinking i just went on amazon and bought an iphone. Will i be able to use that phone with the number i already have?