Android Example: ToneGenerator (via http://goo.gl/5t2s2e)

toneGen1 = new ToneGenerator(AudioManager.STREAM_MUSIC, 100);
toneGen2 = new ToneGenerator(AudioManager.STREAM_MUSIC, 50);

if (toneGen1.startTone(ToneGenerator.TONE_DTMF_1)) {
        Thread.sleep(100);
        if (toneGen2.startTone(ToneGenerator.TONE_DTMF_2)) {
            Thread.sleep(500);
            toneGen1.stopTone();
            Thread.sleep(100);
            toneGen2.stopTone();
        } else {
            toneGen1.stopTone();
            result = false;
        }
    } else {
        result = false;
    }

    toneGen1.release();
    toneGen2.release();
    return result;
}