We have just recently released a cool new app DeFunkt Calls:

★★★ Introducing DeFunkt CallsDeFunkt Calls brings you a newer, modern way to tell if your cell phone call is still active or if you have been disconnected. No more wasted time wondering what happened when the person you're talking to suddenly goes quiet. DeFunkt lets you know right away.★★

Available for Android and Blackberry
I recommend you to download this free and awesome app.