Ok I got it working.... here is what I did so others that might have this problem can do it.
(1) Created an extension on Asterisk example 400 then set the secret for for it and added it.
(2) Added a Sip Gateway in Pbxnsip with the these settings:
Domain: 111.111.111.111 (your ip)
Username: 400 (your ext)
Password: secret(what you set as your secret for that ext)
Outbound Proxy: 111.111.111.111:5060(your server and port)
Remote Party/Privacy Indication: No Indication (not sure if this is important)
Is Secure: yes
(3) Then I set up and extension in Pbxnsip and forwarded that to ext number 7777 (that simulates a call coming in Asterisk)
I set the default incoming trunk in Pbxnsip to forward the ext I made in Pbxnsip that forwards to ext 7777 and bingo! Its working!
Hope this helps someone