Misc. Dialplan Tools three way
From FreeSWITCH Wiki
Barge in the given call, i.e., join some channel to an active call without invitation.
Three way is implemented using eavesdrop and therefore DTMF signals sent by the third party will have the same affect.
<action application="three_way" data="<any uuid of a bridged call>"/>
Or with mod_event_socket:
SendMsg <barge-in initiator uuid> call-command: execute execute-app-name: three_way execute-app-arg: <any uuid of a bridged call>