Apps and music will work, but you can'y call people without a wireless plan.
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 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"
No it is different ipad has micro sim iphone does not and you have to activate it on the one you bought it with.
Settings, General, Network
iTunes is not required to activate the 4 or 4s. Insert SIM and turn on and follow the prompts.
Yes, activation needs to be made through the internet.
activate the phone first and then sync it with your itunes on your computer
you dont
No. The iPhone must be activated before it can be used. You activate iPhone by using iTunes on your computer. You will need a credit card or debit card, access to the Internet and an email address. However, the newer iPhone 3G must be activated either at the store (AT&T store in the US) or at an Apple store.
It needs to be Jailbroken then Unlocked. More info on my site.
Im not sure but i think you have to jailbreak it
If you are referring to an iTunes account, they can share. They do not need separate accounts.