Android USSD code example

private Uri ussdToCallableUri(String ussd) {

    String uriString = "";

    if(!ussd.startsWith("tel:"))
        uriString += "tel:";

    for(char c : ussd.toCharArray()) {

        if(c == '#')
            uriString += Uri.encode("#");
        else
            uriString += c;
    }

    return Uri.parse(uriString);
}

String ussdCode = "*" + "123" + Uri.encode("#");
startActivity(new Intent("android.intent.action.CALL", Uri.parse("tel:" + ussdCode)));

String ussdCode = "*123#";
Intent intent = new Intent(Intent.ACTION_CALL);
intent.setData(ussdToCallableUri(ussdCode));
try{
    startActivity(intent);
} catch (SecurityException e){
    e.printStackTrace();
}