The 2-for-1 Unlimited promotion will post as up to 12 monthly bill credits, as long as you keep the original 2 Unlimited/Unlimited Max lines open on your account.
It will take 2 to 3 monthly billing cycles for your credits to start posting to your account.
If your account is no longer in good standing during the 12-month promotional period, the bill credits will stop and you will no longer be eligible for this offer.