Router running at software level 3.3.1.2_232201.
WAN2 is connected to my virgin modem and works fine.

At what point should the usb light come up if at all?

I plug the usb device in.
No usb light somes on
I configure WAN2 to say 3G usb modem- ok it

select internet access and selec WAN2
I enable the PPP client mode.
Tried seveal APN setttings and the default.
No usb light comes up. No wan2 comes up nothing.
The modem looks likes its doing something, it has a green light come up.

Another question: The usb cable has 2 plugs one end. I can get the modem to work on my PC only using 1 usb plug, but it also works on my Pc using 2 plugs. Obvioulsy the router only has one usb port. Do I need a special cable or something?

Can some one please help... tell what lights they get and when..

After a monumental email trail with support (very helpful they are too) it transpires that the most recent firmware that works with the ZTE MF622 (3 dongle) and my 2820n is 3.3.0.1 (Feb 6th, 2009). Anything more modern, right up to 3.3.4 (RC4A) is broken.

Set the APN as 3internet, and off you go. You may need to trawl the FTP site for the old firmware.

Thats shocking.