[Asterisk-Users] How does one set-up incoming/outgoing SIP with no registration and only IP authentication?

[Frank Tarczynski]

I'm new to asterisk and need some help with ideas to handle this 
configuration question.

I am trying to establish a termination point/DID number in another 
country.  I am currently running Asterisk CVS-HEAD.  My foreign provider 
uses SIP and authenticates via IP address.  I am not required to 
register my SIP connection in order to send or receive calls.

Can someone help me with how to configure this is sip.conf?  My asterisk 
box is behind my firewall.  The current configuration works fine for 
outgoing calls, but has problems with receiving incoming ones.

My current configuration looks like:

[general]
context=default
port=5060
bindaddr=192.168.0.4
srvlookup=no
disallow=all
allow=gsm
allow=ulaw
regcontext=iaxregistrations
localnet=192.168.0.0/255.255.255.0
externip=65.87.XXX.XXX
nat=yes
fromdomain = someone.com

[200.XXX.XXX.XXX]
type=peer
secret=asterisk
host=200.XXX.XXX.XXX
port=5060
allow=gsm
allow=ulaw
context=outgoing
dtmfmode=rfc2833
username=XXX
fromuser=XXX
insecure=very

[from-200.XXX.XXX.XXX]
type=user
host=dynamic
allow=gsm
allow=ulaw
nat=yes
canreinvite=yes
context=outgoing
insecure=very

Thanks,
Frank