How do I determine whether the currently active network connection is Wi-Fi or t

The SCNetworkReachability API allows an application to determine the status of a system's current network configuration and the reachability of a target host. One of the flags returned by the API, kSCNetworkReachabilityFlagsIsWWAN, will tell you if a network connection to the target host uses the carrier network. The Reachability sample code shows how to determine the active network connection.