Carrier [AT&T] Add new line via Next $100 promo...can I switch out sims?

[thenewone]

Regarding this current ATT promo: https://www.att.com/shop/wireless/100-dollar-credit.html#fbid=Qia1TDetYLB

I am going to be adding my sister to my ATT Mobile Share Value Plan. I was also going to be pre-ordering (through Apple, not ATT) the iPhone 6+ for myself at midnight tonight via ATT's Next program. My sister does not care about having a "new" phone, and so I was considering this plan (will it work?):

I add a new line to my plan while purchasing (pre-ordering) the iP6+ via Next for this NEW line (thereby satisfying the terms of the above cited ATT promo). As soon as the phone arrives, I want to swap in MY sim, and move this new line's sim to my old iPhone 5 (which will be going to my sister as the "newly added line").

Does anyone know if this is allowed (switching sims between Next payment plan phones)...and will it still work as far as satisfying the terms of this ATT promo?

If so, this is a way for me to essentially get my iP6+ for $100 off!

 

[thenewone]

Just discovered I would have to (pre-)order through AT&T to ADD a new line via Next. Apple only allows UPGRADING a line via ATT Next.

Still trying to figure out the swapping sims thing though while still receiving (being eligible for) the $100 promo, since part of the promo dictates "Activate a new qualified wireless line of service on your new smartphone." :roll eyes:

Can I simply "activate" the new line on the new phone, and THEN swap sims?