Facebook allowed users on Friday to make free calls to friends at the leading social network using its application tailored for iPhones or iPads. An updated Facebook "app" for the popular Apple mobile devices shows when friends are online and then gives the option of ringing them up by tapping an icon on the screen. Calls are routed over the Internet using telecom service data plans or connections to Wi-Fi hotspots. Facebook introduced a version of the feature earlier this year in its messenger program. Upgrades in the Facebook 5.5 app included a button designed to make it easier to "like" online content and post comments at the social network.