maverick: Mike, your firmware on this device is very very old, the latest is 1.2.5.3, please upgrade your device as this may address the incorrect Content-Length header.
http://www.grandstream.com/firmware.html
Thanks Phil, didn't realise the firmware was old, as I had set the firmware to upgrade on boot, but upon closer inspection the firmware HTTP url was incorrect, so update wasn't happening!
Just updated to firmware 1.2.5.3.
Now the phone registers. :)
However when I make a call to this VFX number (06 8xx xxxx), I get voicemail straight aware.
I can make outbound calls.
Do you have my details at your end and can see why it goes directly to voicemail?