I tried to set a sip truck on Debian8+Freepbx 13, used below setting, but never successful to register with callcentric
[outgoing]
context=from-pstn
fromdomain=callcentric.com
fromuser=1777MYCCID
host=callcentric.com
insecure=port,invite
secret=SUPERSECRET
type=peer
defaultuser=1777MYCCID
disallowed_methods=UPDATE
directmedia=no
videosupport=no
disallow=all
allow=ulaw
[incoming]
1777MYCCID:[email protected]/1777MYCCID