What device are you calling? Is this happening to all devices?
Have you tried to use JabberFree (firstname.lastname@example.org) from a real public IP (without any firewalls between JabberFree and internet)?
Should work: JabberFree > Internet > FW > MCU
In most cases, doesn’t work (depends on the firewall!): JabberFree > FW (on Corp network etc.) > Internet > FW > MCU. This is the normal cause of no media (or Audio only) with Jabber.
So try without any firewalls between, or provide me more information, and I'll look into it.
Hope this helps,