Along with Wi-Fi are new iBeacons, scattered around the park. If you have the MLB Ballpark app, the iBeacons will talk to your phone when you walk into the park.
Located mostly near entrances, the iBeacons will welcome you and offer you some exclusive discounts. The park has plans for the iBeacons, too.
For example, they'd like to put one near the Ty Cobb statue that would send history about the player to your phone.