Hello! I'm pretty much a newbie with all of the "unlocked" iPhone concept. My aim here is to purchase an used iPhone in an excellent condition, so I could send it to someone in Germany. Can he just insert his SIM card to his iPhone just like that? Or are there such certain requirements, so his SIM card would work? One thing I know is that the iPhone itself has to be unlocked; however, I'm seeing so many iPhones by either Verizon or AT&T... so, which one should I choose in this situation? Any suggestions are welcomed as well. Thanks in advance!