1. When we call a busy number wont it detect busy signal?

2. If we get the SIP response code for busy as 486 can we detect the tone?

3. And more over in the client side only we are using softphone, the other end is connected with E1 in the audiocode, so since it seems to be a e1 line here.

The connection is like this,

softphone---> freeswitch----> audiocode---> e1 line.