No
Yes, you need an unlocked & Jailbroken iPhone. Which isn't cheap.
It needs to be Jailbroken then Unlocked. More info on my site.
No
YES it should although if its jailbroken/unlocked it will lock
Not if you are in Canada or the U.S.A. right now.
Sure you can unlock your iPhone 3gs but before that you have to jailbreak iPhone 3gs.
Yes, wether the iPhone is legally unlocked or jailbroken-unlocked.
AT&T SIM card is needed or if jailbroken/unlocked you can use T-MOBILE
if you bought if with orange or have jailbroken and unlocked it then yes is should work fine.
If you haven't saved your SHSH before updating then there is no way to downgrade. Saving SHSH isn't commonly done with iPhone users that aren't jailbroken/unlocked.
Well you would using the Edge network not the 3G so yes It would be a bit slower.
You will most likely have to get a used iPhone from eBay or somewhere, and then get it jailbroken (unlocked) so that you can use any SIM card.