IP Office 500 v2 routing problem

[mezom]

Hello, all.
Pulling my hairs 3rd day...
I try to check WAN port on IPO. In Local network WAN is woking fine. It's working with Phones, Softphones and managing as well.
Now, I put it with real IP address to the Internet directly (made the gap with switch between ISP line and corporate firewall). IPO is pinging from the Firewall, but doesn't ping from the Internet.
Well, I checked the Gap with laptop and another real IP in two modes: with default gateway on NIC and without. The gateway mode is work and without-gateway-mode is not. It's a logical thing and it's right.
So, I try to set the default gateway on IPO. But in any variations there is no result at all.

Please, I really need any advice!!!

Thanks. Nikita.