Only if the iphone is a GSM phone with a SIM card... Otherwise if it is CDMA then no, you have to activate the other iphone.
Im not sure but i think you have to jailbreak it
iTunes is not required to activate the 4 or 4s. Insert SIM and turn on and follow the prompts.
Apps and music will work, but you can'y call people without a wireless plan.
i've had both, and i will never have another phone after having the iphone.
Jailbroken and are not located in the US.
No. You can't activate the iPhone without activating service plan. If you are just looking for the ipod and internet functionality, you should consider the iPod touch
iCloud bypassing is the way to unlock the iPhone activation lock without the Apple ID. You can use this method when you do not know the Apple ID username and Password. The are many free and paid tools for activate the iCloud unlock. use a trusted tool for activate the iPhone lock.
Settings, General, Network
activate the phone first and then sync it with your itunes on your computer
Yes, activation needs to be made through the internet.
you dont
Yes you need to activate it using Itunes, otherwise you wont be able to use it you will only see emergency calls only on the screen or a logo for USB cable pointing to an itunes logo. For the step by step procedure on how to activate iphone, just go the link http://nice-to-know-about-iphone.blogspot.com and look for the topic "Activating an Iphone"