External trunk registration problem

My problem
Can not access and register external sip trunks. any calls using these trunks get the message: all circuits are busy now! this happens after 10/15 sec.

My setup
i have a freePBX(TrixBox) IP PBX setup behind my NetScreen-25. In my setup the modem is in transparent mode and all packets are forwarded to NetScreen, which has its own IP.
I have multiple public IPs setup so in order to make things easier i have assigned an single IP for this purpose using MIP. this public IP points to my internal IP.
then i have created two policies un-trust > trust (MIP) & trust (MIP) > un-trust with the following settings:

Source: ANY/MIP
Destination: MIP/ANY
Services: SIP, VOIP
Application: ignor

Then i have disabled ALG for SIP.

This doesnt seem to solve my problem. i am testing this with two things: 1. if i can register a soft-phone from the internet and 2. if my SIP trunk is registering on my PBX. I am using two trunks, PoivY and CallCentrics
Both of these fail with this setting.

Then i moved to creating custom services with the following ports open:
TCP src port: 5060-5061, dst port: 5060-5061
UDP src port: 5060-5061, dst port: 5060-5061
UDP src port: 10000-20000, dst port: 10000-20000
TCP src port: 5004-5082, dst port: 5004-5082
UDP src port: 5004-5082, dst port: 5004-5082

This also doesnt seem to work at all. i have also tried both options with ALG turned on with no luck.

in addition i have read on some other forms that i must add these lines to sip.conf.

any idea what i am doing wrong? i am quite sure that the problem is in the firewall somewhere but not 100%. could it be in the PBX setting?

Do you have a double NAT (Router - NetScreen-25 - LAN) ?

If so, create a static route from LAN to Router

NAT 1 (router to Netscreen) = 192.168.2.xxx gw,
NAT 2 (Netscreen to LAN) = 192.168.1.xxx gw ,

to create a static route from LAN to Router:
sudo route add -net netmask gw

Also, I recommend to put your asterisk server under “DMZ” from NetScreen-25

good point, my netscreen is behind a router/modem(provided by ISP). the modem however is in transparent mode, so there is no need to do this is there?

If the router is in transparent mode, the public external IP shoud go straight to the NetScreen wan interface.
The other interface of netscreen (lan side) shoud be the gateway for the asterisk pbx.