if you bought if with orange or have jailbroken and unlocked it then yes is should work fine.
yes. once an iphone is universally unlocked it will work.
Yes
no unless it is unlocked... .
No it wont
Yes it will. I have mine with Centennials service
yup get it unlocked and you good to go!
No sorry the Iphone uses a different type network than the Nextel service.
No
YES it should although if its jailbroken/unlocked it will lock
Assuming the SIM card is the correct size for the iPhone (ie not a micro SIM) - there's no reason why not. Since you say it's unlocked - it should accept any networks SIM card.
No