SIP Carrier

Hi, I would like to ask your opinions regarding SIP Carrier. Is it a must that a SIP carrier must have a FQDN? and is it must also has SSL? Thank you for your response.
VICIDIAL astGUIclient discussion forum
http://forum.eflo.net/VICIDIALforum/
http://forum.eflo.net/VICIDIALforum/viewtopic.php?f=7&t=40542