Wi-Fi calling lets customers use their voice and messaging services over home, office and public Wi-Fi networks. With Wi-Fi Calling, you can get improved voice, data and messaging services in locations that have limited or no mobile network coverage. All domestic calling and messaging is free (standard CDMA international rates apply for international calls).
The software update notification will be pushed automatically to these customers during the next few weeks. Sprint plans to expand Wi-Fi calling to additional devices in 2014.