So I have 3 units coming on Friday all for AT&T. Two apple store and one direct from AT&T. All 3 upgrades using next. Do I need to activate each with the line it was assigned to? In other words I might decide I don't want the plus so want to switch it with my sons 4.7. Do we activate each with the new sims that I assume come in each and then switch them later if we decide to switch phones or can we just choose which one we each want and then change sims prior to activating?. Or do we even need the new sims as opposed to just putting in our current ones into the units we each decide on and then activate? Thanks in advance.