Settings, General, Network
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.
iPhone 3g is capable of 3g access, but not iPhone 1st generation. However, some areas do not have 3g coverage, so iPhone will automatically switch to EDGE. iPhone 1st generation only has EDGE and Wifi, and iPhone 3g has EDGE, 3g, and WIFI.
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
Yes u can
When you activate an iPhone using iTunes, you will be required to sign up for an AT&T calling plan to unlock the iPhone. There is a minimum required plan to sign up for service with AT&T. You will also want to add AT&T's unlimited data plan, as accessing visual voicemail as well as surfing the web while not connected to a Wi-Fi network will use the EDGE network, which will lead to an enormous bill without the Data Plan. You can also activate the iPhone on a GoPhone plan through AT&T/Cingular, but this will also require adding minutes.
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"
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.