I have an IPhone 3Gs and my dad got the 4s and gave me his 4. What I was wondering is since the 4 has a smaller sim card can i just use the sim that is in the 4 even though it was on my dads number. if so how would you do that? My idea was you could plug the 4 into itunes with the old sim that was never mine in it, and set it up as my phone and backup, within itunes. Could/will this work?