How Set Idle time on phones connected to one raspberry pi 3 ( Interruption )

Hello Everyone,

I will be so happy if someone can help me for a solution on my case ,

I have Raspberry pi UP with asterisk and all proper config for sip trunk and phones, I can make calls from soft-switch and its goes on Pi3 and then dial on phones can have my call over VoIP successfully .

Now my issue is that I have 4 connected phone and I want to distribute calls between phones, as the calls always go on the first phone and if the second call come then next phone, Or any solution that i be able to set idle time for a phone that had one call and give interruption for next call .

Hope someone help me if there can be any way to let a phone be idle after had some outgoing calls and pi send the call on another phone :frowning: