Can someone help me? I have a Droid 3 with unlimited data. I just bought a Droid 4 (used). Is a SIM card needed for that to make it work? If I'd have to get one, I assume that I'd need to call to activate the phone after inserting the SIM card. Will I still have my unlimited data or will that go away because I upgraded to a 4G phone? If I visit another country and buy a SIM card there, would that allow me to connect to their 4G network? Thanks!