You can use the following to help configure the VoIPtalk ID to the Trunk details on your PBX.
[VoIPTALK]
host=voiptalk.org
insecure=peer,invite
secret=[voiptalk password]
type=peer
username=voiptalkID
disallow=all
allow=ulaw&alaw
allow=G.729
outboundproxy=nat.voiptalk.org
outboundproxyport=5065
fromdomain=voiptalk.org
canreinvite=no
registersuffix=voiptalkID
fromuser=voiptalkID
Registry:
voiptalkID:voiptalkpassword@VoIPTALK/voiptalkID