The only aspect of VoXaLot's Call Forwarding that I have experience using so far is the default rule (by itself) to forward all incoming calls to another destination. An example would be having all your VoXaLot incoming calls forwarded to your Gizmo Project (Sipphone) provider using the following default rule:
sip:1747xxxxxxx@sipphone.com (xxxxxxx is the remainder of your phone number at Sipphone)
It's possible, however, to forward only calls that match a particular CallerID pattern. To accomplish this, you would use what's known as a Regular Expression pattern match string to select which calls to forward. You can have up to nine matching patterns, each with its own destination.
If you're not familiar with composing Regular Expressions, there is a good tutorial at
http://en.wikipedia.org/wiki/Regular_expression.
Ron