[Asterisk-Users] Pickup zap channel already in use?

[Kent]

I am using asterisk at home with a Cisco ATA186 and a clone X100P card.
My inbound telco line is plugged into the X100P card.
My telco line is also plugged into other phones in the house for now
so someone else can answer the phone without asterisk being involved.

What I would like to do is if someone has answered the call on a
normal phone in the house I would like to be able to join the call
from a SIP phone by dialing an extension or feature code.

Is there any way to do this?

Thanks in advance.