Iaxy configuration - Iaxy will not connect to Asterisk

I have successfully provisioned an Iaxy and configured it to talk to an Asterisk server. When this iaxy is plugged into the network where the asterisk server resides there seems to be no issue. I can pick up the handset and dial the extension, and the analog phone plugged in to the iaxy will ring. If I take the iaxy to another physical location and attach it to the broad band connection directly (No router, and service provider issues a DHCP address), the iaxy cannot go and find the asterisk server and as such the extension doesn’t ring and goes straight to vmail. Any ideas???

I presume that your Asterisk lives behind a firewall.
Have you set your firewall such that you port-forward ip traffic coming in on the IAX/2 port toward your Asterisk?