I'm having trouble configuring Call Barring.

I want to prevent calls to premium rate numbers, and international calls; although it would be useful to enable international calls on a specific extension on an ad-hoc basis or at least only during business hours.

The manual only makes mention of Call Barring vs URI/URL or a specific number - but I've not found any explanation of what format a URI/URL takes!

Incidentally, I've configured a wildcard dial plan to enable a default SIP route. This is important to keep, but I'm unsure how this will interact with any Call Barring configuration.

Advice and/or online resource would be most appreciated.