How to use 3G Connection in Android Application instead of Wi-fi?

/**
 * Enable mobile connection for a specific address
 * @param context a Context (application or activity)
 * @param address the address to enable
 * @return true for success, else false
 */
private boolean forceMobileConnectionForAddress(Context context, String address) {
    ConnectivityManager connectivityManager = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
    if (null == connectivityManager) {
        Log.debug(TAG_LOG, "ConnectivityManager is null, cannot try to force a mobile connection");
        return false;
    }

    //check if mobile connection is available and connected
    State state = connectivityManager.getNetworkInfo(ConnectivityManager.TYPE_MOBILE_HIPRI).getState();
    Log.debug(TAG_LOG, "TYPE_MOBILE_HIPRI network state: " + state);
    if (0 == state.compareTo(State.CONNECTED) || 0 == state.compareTo(State.CONNECTING)) {
        return true;
    }

    //activate mobile connection in addition to other connection already activated
    int resultInt = connectivityManager.startUsingNetworkFeature(ConnectivityManager.TYPE_MOBILE, "enableHIPRI");
    Log.debug(TAG_LOG, "startUsingNetworkFeature for enableHIPRI result: " + resultInt);

    //-1 means errors
    // 0 means already enabled
    // 1 means enabled
    // other values can be returned, because this method is vendor specific
    if (-1 == resultInt) {
        Log.error(TAG_LOG, "Wrong result of startUsingNetworkFeature, maybe problems");
        return false;
    }
    if (0 == resultInt) {
        Log.debug(TAG_LOG, "No need to perform additional network settings");
        return true;
    }

    //find the host name to route
    String hostName = StringUtil.extractAddressFromUrl(address);
    Log.debug(TAG_LOG, "Source address: " + address);
    Log.debug(TAG_LOG, "Destination host address to route: " + hostName);
    if (TextUtils.isEmpty(hostName)) hostName = address;

    //create a route for the specified address
    int hostAddress = lookupHost(hostName);
    if (-1 == hostAddress) {
        Log.error(TAG_LOG, "Wrong host address transformation, result was -1");
        return false;
    }
    //wait some time needed to connection manager for waking up
    try {
        for (int counter=0; counter<30; counter++) {
            State checkState = connectivityManager.getNetworkInfo(ConnectivityManager.TYPE_MOBILE_HIPRI).getState();
            if (0 == checkState.compareTo(State.CONNECTED))
                break;
            Thread.sleep(1000);
        }
    } catch (InterruptedException e) {
        //nothing to do
    }
    boolean resultBool = connectivityManager.requestRouteToHost(ConnectivityManager.TYPE_MOBILE_HIPRI, hostAddress);
    Log.debug(TAG_LOG, "requestRouteToHost result: " + resultBool);
    if (!resultBool)
        Log.error(TAG_LOG, "Wrong requestRouteToHost result: expected true, but was false");

    return resultBool;
}

And this for calculate host address:

/**
 * This method extracts from address the hostname
 * @param url eg. http://some.where.com:8080/sync
 * @return some.where.com
 */
public static String extractAddressFromUrl(String url) {
    String urlToProcess = null;

    //find protocol
    int protocolEndIndex = url.indexOf("://");
    if(protocolEndIndex>0) {
        urlToProcess = url.substring(protocolEndIndex + 3);
    } else {
        urlToProcess = url;
    }

    // If we have port number in the address we strip everything
    // after the port number
    int pos = urlToProcess.indexOf(':');
    if (pos >= 0) {
        urlToProcess = urlToProcess.substring(0, pos);
    }

    // If we have resource location in the address then we strip
    // everything after the "https://stackoverflow.com/"
    pos = urlToProcess.indexOf("https://stackoverflow.com/");
    if (pos >= 0) {
        urlToProcess = urlToProcess.substring(0, pos);
    }

    // If we have ? in the address then we strip
    // everything after the '?'
    pos = urlToProcess.indexOf('?');
    if (pos >= 0) {
        urlToProcess = urlToProcess.substring(0, pos);
    }
    return urlToProcess;
}

/**
 * Transform host name in int value used by {@link ConnectivityManager.requestRouteToHost}
 * method
 *
 * @param hostname
 * @return -1 if the host doesn't exists, elsewhere its translation
 * to an integer
 */
private static int lookupHost(String hostname) {
    InetAddress inetAddress;
    try {
        inetAddress = InetAddress.getByName(hostname);
    } catch (UnknownHostException e) {
        return -1;
    }
    byte[] addrBytes;
    int addr;
    addrBytes = inetAddress.getAddress();
    addr = ((addrBytes[3] & 0xff) << 24)
            | ((addrBytes[2] & 0xff) << 16)
            | ((addrBytes[1] & 0xff) << 8 )
            |  (addrBytes[0] & 0xff);
    return addr;
}

And following permission must be added to AndroidManifest.xml

<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
<uses-permission android:name="android.permission.CHANGE_NETWORK_STATE" />

It works only with android 2.2 and above, tested on both Nexus One and on LG Optimus, other phones I don’t know because some method of ConnectivityMananger are vendor-specific.
After 15-20 seconds of inactivity, mobile network is automatically disconnected.