[Freeswitch-users] Doubts with att_xfer

Hi, I am trying to enable att_xfer for calls that come from pstn, these call are being routed to an internal registered SIP Phone. In asterisk I had those options "Tt" in the Dial application to enable transfer to the caller party and to the calling party. The question is that for internal call I want both legs be able to transfer to whoever they want, but for external calls I want just the internal leg be able to transfer calls. How can I do that? Regards.