Pardon the necrobump, but in case anyone else is looking these are some settings that worked for me:
type=friend
dtmfmode=auto
username=ACCOUNT_SUBACCOUNT
secret=PASSWORD
context=from-trunk ; (this could be ext-did or from-pstn as well)
insecure=port,invite
canreinvite=no
host=inbound17.vitelity.net
#
ACCOUNT_SUBACCOUNT:PASSWORD@inbound17.vitelity.net:5060
#