SIP Trunk w/ SIP Proxy?

Hello. Can anyone point me in the right direction on setting up a SIP trunk via a SIP proxy? We have siproxd running on our NAT. The PBX in a Flash box is behind the NAT and is unable to connect properly to our SIP provider, as it must use the proxy.

Here are the settings we have:

type=peer username=****** secret=***** fromuser=**** (same as username) context=from-trunk disallow=all allow=alaw&ilbc&ulaw insecure=port,invite qualify=no port=5060 nat=no aut=md5 canreinvite=no dtmfmode=rfc2833

Register String:


Where do I define the SIP host, username and password to use?