If you dial a number and hear the message 'You are not authorized to call dialed destination' it means that dialed destination is not allowed for your xxtension. In order to change allowed destinations:

• Login to the system administration
• Navigate to 'Extensions'
• Click on 'Edit' next to the extension
• Click on 'Destinations'
• Click on 'Set Destinations Manually'
• Navigate through 'Remote Destinations', 'Local Destinations' and 'Other Networks' and set allowed destinations for that extensions
• Click on 'Save'