Using the code that Apple has provided here
Reachability *reachability = [Reachability reachabilityForInternetConnection];
[reachability startNotifier];
NetworkStatus status = [reachability currentReachabilityStatus];
if(status == NotReachable)
{
//No internet
}
else if (status == ReachableViaWiFi)
{
//WiFi
}
else if (status == ReachableViaWWAN)
{
//3G
}