alexd was thinking very hard :
[color=blue]
> Workaround of the Day: Install Asterisk. Register a free Sipgate account for
> incoming calls and a voip.co.uk for outbound. Do call diverts and voicemail
> on your Asterisk box. Job done![/color]

Not so effective if the reason for needing the forward is because the
connection to the ITSP is down.