Can I use a AT&T iPhone on the go phone at&t without unlocking it?

I'm going to buy a AT&T iPhone on Craigslist and I want to be able to use it on the AT&T go
phone. I don't really know what "unlocking" means so if you could please describe that or tell me I
don't even need it to use it on the go phone that would help a lot! Also if you do know describe how i can put it to a go phone plan!

Where can i sell my expensive iphone 4 case?

I have a 100% real swarovski crystal pink iphone case by deo.s so it's legit. I payed over 300 dollrs for it in NYC and i don't have my iphone anymore so i'm freaking out about how to sell this in order to get some money to buy another iphone. I really have been trying everything and i don't know what to do please help!

Where to watch The Walking Dead on the iPod touch/iPhone?

Is there a good website where I could watch the series the walking dead on my 4g iPod touch for free? Preferably the full series, but if I could get just the first season that's fine. And if it requires adobe to watch it, that doesn't work on the iPod.

Save a video from kik?

Someone sent me a video on kik that I want to download and save but I can't find out how. I hae to view it in an app called Video for kik (iphone) but i can't find anyway to save it. Anyone know how?

Does imessage say text message if the iphone is off?

Hopefully someone who knows about the iphone can answer this. IPhone to iPhone usually says "iMessage" when you text(blue send button).So lets say your phone dies or it is off does the person texting you still see "iMessage" or will it change to "text message" since the phone is off?