Here is excerpt from my code (it works so far):
ConnectivityManager connManager = (ConnectivityManager) getSystemService(CONNECTIVITY_SERVICE);
NetworkInfo mWifi = connManager.getNetworkInfo(ConnectivityManager.TYPE_WIFI);
NetworkInfo mEthernet = connManager.getNetworkInfo(ConnectivityManager.TYPE_ETHERNET);
NetworkInfo m3G = connManager.getNetworkInfo(ConnectivityManager.TYPE_MOBILE);
if (mWifi!=null) isOnWifi = mWifi.isConnected();
if (mEthernet!=null) isOnEthernet = mEthernet.isConnected();
if (m3G!=null) is3G = m3G.isConnected();