It depends on your scenario and purpose, you can do that in scscf and icscf.for example you can see pstn routes in icscf and scscf and even you can define an mmtel in hss for routing your calls by scscf by reading the ifc and spts that scscf gets in saa from hss

On Mon, May 20, 2019, 15:08 Mary Honey <maryhoneyplus@gmail.com> wrote:

Hello everyone,
I install and setup an IMS Network by kamailio-5.2.2 . I have p-cscf, i-cscf and s-cscf in three different systems . my Hss is Fokus. Registration and call between subscribers of network work successfully . now I want to define IP Trunk in my network which can pass external calls through my IMS network. I don't know how to define IP Trunk and changes in which element(pcscf, icscf or scscf) should be done.

_______________________________________________
Kamailio (SER) - Users Mailing List
sr-users@lists.kamailio.org
https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users