You could do this using the Auto Attendant in CUE.
Dial into CUE with dial in number and have extension transfer setup.
Within the script allow enough digits for ( extension transfer ) ie in the U 01903 777777 11 digits, and then you can dial out to any number as long as their is a dial peer matching the outbound number.
Scripts are located in system / scripts ( upload as necessary ) Script parameters are controlled in voicemail auto attendant By default Cisco CUE has a default script with enable external transfers set to false. If you enable this you will be able to make external calls. Provided dial peers are correct.
Script design and modification will not be elaborated on as this is a specific and complex subject issue. However the default script will do what do what you need unless it has been edited.