Yes.
It is now legal to unlock or jailbreak a iPod, iPhone or iPad in USA. <Edited By dontbother> By buying a Pay As You Go iPhone 4 it is unlocked to any network already (UK Only)
You can get it from websites or phone shops. Visit network provider websites to find their current pay monthly and pay as you go rates for an iPhone 4.
if you want pay 20 bucks if your desprate or just wait
An iPhone 4 can be purchased at any carrier of the iPhone. And any Apple in-store or online store.
No
If you have the iphone 2g(the one with black and white back cover),then the answer is no..But if you have iphone 3 or 3gs,they will let you upgrade the phone to iphone 4 as long as you pay for the new iphone 4. Hope this Helps. And by the way,if the iPhone is Jailbroken,or unlocked,then they won't let you upgrade it. so make sure you restore your iphone before you trade for a iphone 4
So far there is no emulator software for the iPhone 4 or any other iDevice.
No
I'm assuming this is old as the iPhone has been out awhile, but no there is no return policy with Apple or AT&T.
any
It will depend on where you rent/purchase the handset from.
yes