"Dial Policy" or "Call Barring" applies to Outbound calls for you and your users. To allow calls to dial high-cost and internationally, you must first allow this permission.
Barred Destinations works on a whitelist principal whereby you must allow destinations to call.
By default, your organisation may call UK Landlines (01, 02 & 03) and UK Mobiles. If you wish to allow other destinations or "Allow All", navigate to "Dial Policy" in the portal and select the destination you wish to allow calling.
UK has been categorised into various destinations.
International calling is limited per country. This means user's may call ANY destination in this country, including high-cost destinations.