One to One conferencing

I want to realize one scenario but i dont know how, maybe someone can advice.

I want incoming call to have ability to choose 1 or 2 (I have realized it)

after i want to connect 1’s to 2’s and let them to talk one to one.

ie if 2 people choose 1 and one person choosed 2 then i should get 1 pair talking and one person waiting for incoming call who will choose 2.

I did conference but i dot want all people to communicate with each other.

Not sure whether asterisk an open source software can be implemented for intercom without internet. I am using appliance from right now but have many of clients/friends who use Asterisk…