Detect if an outgoing call has been answered
I don't think there's such API and also there's no API for sending DTMFs due to the same reason that you can't tell when the call is being connected.
It does not necessarily needs to be possible to capture this as an outside app. The green android icon is a part of the application that controls the call, so it does not need a broadcast to change the icon.
As far as android's telephony manager is concerned u cannot detect programmatically whether the call has been answered or not. This is to say that u do not have the option to know when the user picked the phone at other end.Android has got 3 states of telephony manager and none of them are capable of detecting whether the call was actually answerd or not(IN CASE OF OUTGOING CALLS)