IChat only works when I make phone calls??

Question

Ok, so this is getting absolutely ridiculous. My ichats constantly disconnect after about 30secs each and every time i start a conference from my Macbook Pro in the UK to my parents iMac located in Norway. Both running Leopard 10.5.5 and with the latest software upgrade (including the ichat/quicktime 7.5.5 fix released on 17nov)
I've got a Netgear wireless router DG834G with latest firmware installed.
I've opened up all the ports on the router recommended by apple. I've done this while UPnP is off. I've also tried turning on UPnP and closed the ports.
We've both tried setting bandwith limit to 500, and quicktime streaming settings to 1.5mbps with no luck.
Internet sharing is off on both sides.
Both tried ports 443 and 5190 in ichat prefs.
I've tried turning "Respond to Ping on Internet WAN Port" on and off in the router setup.
I've tried the connection through Ethernet instead of wireless.
We're both logged in with AIM accounts.
NOW, the interesting bit is this: when I make a phone call on my landline from the UK to Norway and start an iChat conference, it works like a dream! Smooth crisp video and audio and no interruptions! As soon as either of us hang up the phone, our ichat connection freezes and we both get the error -20 (no audio video for 10 seconds etc..) It is as if our phone has opened some sort of direct connection by which our video chat can travel alongside?
Same thing happens to audio chats.
Connecting to [email protected] however, works fine.
My internet connection is going through the Netgear router to a Time Machine (set to bridge mode) providing me with the wireless connection. I'm with Toucan ISP in the UK.
So basically, what we were trying to avoid in the first place (making expensive phone calls) is now the only option to maintain a video conference. So much for convincing my parents how reliable their brand new expensive mac is.
Please if anyone can make sense of this I'd be very grateful for your help!

Answer 1

I agree with Defcom that a Dodgy Micro-Filter looks like the first choice to check out.
I also can't see that you disabled the DOS or SPI setting on the WAN Page in the Netgear.
DOS can see the amount of data iChat sends as an Internet Attack and will cut the one port that the data is being Streamed on to protect your Internet Connection.
SPI checks to see if the data is "Valid" and iChat seems to be able to send data faster that it can cope. On some Devices DOS is also a part of any SPI firewall it may have somewhat adding to the issue.
I used o run the Netgear DG824G with the Allowing Pings and Disabling DOS using UPnP.
8:41 PM Sunday; November 30, 2008