Good thread you have going here.

I have extensive experience using GizmoProject with devices (including N800), and several home routers.

First I have to tell you that even with the N800 IP address DMZ'd I have trouble with SIPPHONE regardless of whether I used the N800 built-in client ( RTCOMM ) or the Gizmo Client. This problem extends to desktop computers trying to do SIP thru certain routers.

It can get complicated...... one of my routers is the popular Linksys WRT54G (version 5). This Linksys router uses synchronous NAT, and I read somewhere that this doesn't work well with STUN. I also know that GIZMO does NOT work with outbound proxy. Outbound proxy is what you'd use if your router has synchronous NAT. Outgoing proxy is an alternative to STUN. Sooooo, my WRT54G didn't operate as it should with STUN ( synch. NAT issue ) and Gizmo Project doesn't allow any outbound proxy. What to do??

I also have a "device" known as a Sunrocket 6011S. I spent many hours struggling with this trying to get it ( and / or the N800 ) to work nice with SIPPHONE ( GIZMO ). I learned that if I placed the Sunrocket 6011S on the public side of my Linksys WRT54G all worked as expected. There was a problem with Bittorrent going thru the 6011S but explaining that will get me way off track here. I also spent much time with the AC211, it is another Sunrocket device.... an ATA with RJ11's. Anything on the private side of my WRT54G was a problem ( N800, Gizmo desktops, 6011S, AC211). I also spent quite a bit of time with SJ_Labs SIP soft client configured for Gizmo on the private side of my router.

My neighbor allowed me to use HIS wireless network. He has a similar (but not identical) Linksys home router. He has the WRT54GS (speedboost). What I learned from this test is that his WRT54GS was "friendlier" to my SIP "devices" than my WRT54G. I could do all kinds of things on the private side of HIS network and SIPPHONE worked well. I did a USB wifi link to a laptop (my neighbors network), then bridged (XP) that to the Ethernet port on the laptop and connected the Sunrocket AC211 and the Sunrocket 6011S with success.

Everything was pointing to my Linksys WRT54G as the common denominator causing the problem(s).

What to do?? I looked for a router to replace mine but I wanted to be sure to get a new router with asynchronous NAT, as this is what STUN needed, and STUN is what SIPPHONE/Gizmo needed. Finding a router I could be certain was asynchronous NAT wasn't easy. What was easy was flashing my WRT54G with aftermarket firmware to see if that might fix things for SIPPHONE.

Result? Yes, after replacing the firmware in my Linksys WRT54G with non-Linksys firmware I can now have ATA devices (AC211 and 6011S) and or the N800, on the private side of my router (no longer a pure Linksys) and use GizmoProject / SIPPHONE. I used the popular DD-WRT. This is not an endorsement of DD-WRT, I am simply stating what I did.

I took many hours of troubleshooting and digging through many forums to formulate the solution. No place had I read specifically to do what I ended up doing. It was a culmination of information gathered from the Internet and from my experiments thru my neighbor's router which eventually pointed me to trying the firmware swap. I suppose a different router make and model might have worked also, but that was a crapshoot if I had to buy every router model trial and error. (I guess I could have purchased a WRT54GS.)

I see where the OP ( godd ) mentioned his router model. I don't have specific information about that router, but if you are having audio-in or audio-out problems with SIP it is most likely NAT related. Home routers are designed to block your network so those in the wild can't see anything on the private side. Port Forwarding and DMZ techniques are "supposed to" open up a path, but I can testify that these did not work properly with my WRT54G in stock trim. Another headache is that in order to properly DMZ a device, you must know it's IP address on you private network, and that can change if you allow/use DHCP. Making every IP "fixed" (static) is also a pain in the butt if you change equipment constantly like I do.

BTW- The VOIP firm Sunrocket went out of business in August 2007 and there is much Sunrocket hardware on eBay these days and it can be bought very cheaply. People don't want it, or it is surplus new in the box from retailers who pulled the stuff and dumped it to liquidators. The 6011S is an extremely well build wireless IP Phone, which works well with Gizmo, and other SIP providers once you reconfigure it away from Sunrocket. I have three of these 6011S IP phones, and I sent my buddy a Sunrocket AC211 ATA. I use the N800 or a 6011S or the Gizmo client for Linux or Windows on desktops here everyday. Once I resolved the router issue, all works well. I hope this information helps you.

M5