try {
   Intent intent = new Intent(Intent.ACTION_CALL);
   intent.setData(Uri.parse("tel:+123456"));
   startActivity(intent);
} catch (Exception e) {
   Log.e("SampleApp", "Failed to invoke call", e);
}

try {
   Intent intent = new Intent(Intent.CALL_ACTION);
   intent.setData(Uri.parse("tel:+123456"));
   startActivity(intent);
} catch (Exception e) {
   Log.e("SampleApp", "Failed to invoke call", e);
}

http://www.lacherstorfer.at/haris_blog/2008/03/android-howto-invoke-a-phone-c.html

a 2-lines code to start a phone call from your Android application

Start a phone call from Android application

phone, android

Java