I'm sure AT&T ol'timers already know this; but I just found out tonight. If you're on certain plans (e.g., the Family 1400 plan that I'm on), you've got a feature called "A-List," which lets you specify up to 10 numbers (landline or cell) for unlimited talk time. As such, I was able to add folks like my parents, the DrMS's parents, and a few different friends who aren't on AT&T ... and now we'll get unlimited talk time with them.
Just wanted to share as an AT&T newbie.