Where can I buy an unlocked iphone in Miami?

I'm going to travel to Miami next month, and i want to buy an iphone, but it has to be unlocked, otherwise I won't be able to use it in my country. I was searching online in best buy and wallmart, and I want to know if someone could recommend me another place to look.

Can i use my sim in an iphone 3gs?

So my friend said he will sell me his old iphone 3gs on O2. My sim card i O2 Pay as you go, his was contract. So if i restore the iphone and put my sim in will it still work? Also does i run IOS 1.6.3?

How to fix this problem? (iPhone 3GS problem)?

So I just updated my iPhone 3GS to iOS 6. And about 3-5 minutes the battery life completely dies. My mother won't let me replace the battery so what do I do without replacing or removing the battery IN the phone?

What to ask for, for Christmas (teen girl)?

I'm looking what to ask for, for Christmas. I don't need a lot of things but my mom always likes to buy me a few gifts. I'm very grateful for everything I have already, so suggestions for cool things that a teen girl would like would be awesome.
I'm into dance, music, fashion, beauty, etc.
I already have an iphone, a great bedroom, a good amount of shirts, low-end branded makeup, which I'm totally thankful for all those things.

Do I need a new iPhone 4 charger?

My phone isn't charging. Till yesterday it used to say This accessory is not supported when I touched the charger or moved my phone. But now it's not charging at all… I'm pretty sure it's the charger because the rubber thing is ripped at the end and you can see the wires from inside, and also my friend gave me her charger and it was charging. So it's the charger. But do I have to buy a new one? Because I need my phone, I don't really have time to buy a charger, since I live far from the city, and I can't just go whenever I want, and also I'm not in very good condition with my money… I don't have other chargers that can charge my iPhone, and I don't have any friends who live nearby to borrow their charger. So do I HAVE to buy a new one or is there any way that I can charge it differently?