AT&T -> AT&T was always unlimited under my plan. The new incentive allows you to call ANY mobile phone without using your minutes.
We have so many rollover minutes that this makes no difference for us. My calling plan is so old that it is grandfathered in. I've been with AT&T since my husband bought me my first cellular phone in the '90s. The thing looks like the one that Gordon Gekko gets when he leaves prison in Wallstreet 2.