What carriers can the iphone 3gs be flashed to?

I have recently purchased an iphone 3gs and i would love to be able to unlock it and somehow use it on a pay as you go plan?
my first thought was to unlock the iphone and use it for virgin moble because there plans are the cheapest, but then i figured out that virgin mobile phones don't have sim cards…
If i got a at&t pay as you go phone, and stick that sim card into the iphone would it work?
are there any other carries that would work?

Is 3G the same price as Edge on an iPhone?

I pay for unlimited internet & data, so I turned on Cellular data. Right now, my phone has an "E" (edge) in the corner instead of 3G. I was wondering if i turned 3G on, would it be the same price as my E or will it cost money

What will happen if i update my iphone 4 to IOS 6.1?

An update appeared in settings and i wanna know what will happen. Last time i updated it to IOS 6 and it made my iphone slower and its battery life shortened. It also turned the maps app from google maps to TomTom maps and now there's no street view. Any way let's get back to the REAL question. What will happen to my iphone when i update it?

What Zoom is best for my iPhone 5?

I'm going to a music concert next week so i decided to buy myself a extra zoom for my iPhone 5 on ebay so my pictures will be able to see closer and be more clear instead of buying a camera, but as i have come to buy the zoom it has gave me 2 options, Aluminum Zoom and Optical Zoom. What is the difference and what one would be most suited for me?

Hope you can help, thank you!

Why don't guys respond to texts?

So I was just texting some guys ( i don't like them in that way) but they have Iphones and so do I. So I was texting them and after a little conversation, they didn't reply but it showed that they read it. Can someone please tell me why they do that? Or if you type alot, they just say "yea" or "nice". I don't have a crush on them but I was just wondering.

Added (1). I don't think i'm annoying, i mean i don't send them more then one text at a time. I just try to make conversation.orr when we're in the middle of a conversation, he sees it but doesn't reply.

How to put music from iphone onto iTunes?

There's this music on my phone from one iTunes on one profile on the Mac desktop. How can I put that music in a different iTunes of a different profile on the same Mac