I pre-ordered the iphone 5 and i got a great offer on my iphone 4 that i'd like to jump on before it's too late. My sister gave me her old iphone 3 that she doesnt use anymore. I plan to use this temporarily until the iphone 5 arrives. Do i just take out my sim card and put it in the iphone 3? Is that all it is or do i have to get it activated, or back up anything, or save contacts, etc...? Thanks!