How can i setup a phone to ring even if the phone is in use. I have setup a ring group to ringall

For testing purposes I have 2 phones
Phone 1 has extensions 100,101,102
Phone 2 has extensions 200,201,202

I put all extensions in a ring group and when I call from outside both phones ring.
When I am using any extension on Phone 1 and call in only phone 2 rings.

I need the next free extension on phone1 to ring as well.

Phone 1 would be a main receptionist phone and should get all the calls but I still need all phones to ring.

How can I set this up?


Turn on Call Waiting for that extension.