iTunes is not required to activate the 4 or 4s. Insert SIM and turn on and follow the prompts.
activate the phone first and then sync it with your itunes on your computer
you dont
If you are referring to an iTunes account, they can share. They do not need separate accounts.
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"
you can, but only with an iTunes gift card
yes, it activates through iTunes. Which requires an Internet connection
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.
Yes, restore it to factory settings by pluging it into iTunes first before taking it to AT&T
You can add a video on YouTube without going through iTunes on your iPhone by uploading it directly via your PC.
You can without but the easiest generally do use iTunes.
Im not sure but i think you have to jailbreak it
Itunes on the iPhone is preinstalled.