Launch an app from within another iPhone

Question

Is it possible to open any iPhone application at random from inside another app? , For instance, in my application, if I want the user to click a button, the Phone app will open immediately (close the current app, open the Phone app).

Was it possible to do that? I am aware that the tel URL link may be used to make phone calls, but I would prefer to launch the Phone app directly instead of first dialling a number.