AT&T’s grandfathered unlimited plans are vestiges of an earlier era, when unfettered access to mobile data was a perk offered to those willing to buy into the smartphone before it became ubiquitous. AT&T has just announced a $5 increase on its grandfathered unlimited plans, bringing the total cost per month to $40, according to a report from DSLReports yesterday and confirmed by ArsTechnica today. The price hike won’t occur until March 2017.