These are the settings I am using on my sipgate trunks and they show as registered and work fine.
username=myusername
type=peer
secret=MYPASSWORD
registerattempts=0
qualify=yes
nat=force_rport,comedia
insecure=very
host=sipgate.co.uk
fromuser=myusername
fromdomain=sipgate.co.uk
dtmfmode=auto
disallow=all
context=from-trunk
canreinvite=no
allow=ulaw&alaw
My router has 5060 UDP and 10000-20000 UDP forwarded to my PBX internal IP