> 400 means bad request.[color=blue]
>
> What kind of router do you have?[/color]

Many thanks. It's a netgear DG834.
[color=blue]
> Maybe there is a SIP ALG in your router that is mangling the SIP on the
> way through.[/color]

I don't think there is anything in the router's configuration about SIP. I
don't understand what ALG is.