Alright so my friend can get me a brand new iphone 3gs activated in the store. i want to buy the phone off of him and he wants to use the simcard with an other phone.

Can i unlock it 3.1.3 ?
Can i downgrade it then unlock it ?
Can i use the iphone 3gs as an ipod without a simcard and not unlocked?
Can i sync my music with itunes without a simcard and not unlocked?
Can i jailbreak my iphone without a simcard ?

Thanks