Is it possible...? (uide soon as possible)

We are dialing a zap channel by using a .call file. We want to play some background to that zap channel when the phone is picked up.
Following happens now…
The phone on zap channel rings. We picked up the phone but some of the background has been played even though we are using a wait of 5 seconds after answer to play the background.

exten => s,1,Answer
exten => s,2,Wait(5)
exten => s,3,Background(some file here)

Now the point of confusion is when we have to pick the phone then is there any need of “Answer” application (exten => s,1,Answer)??? If no, then how we will know that the phone has been picked up???