Since you are getting an error like Cause i = 0x8281 – Unallocated/unassigned number it implies that there is a problem with the syntax that you are using for outbound calls. are you using the e.164 scheme? are you placing your calls with a numbering like 00442073403621?
when you use this numbering scheme to make outbound calls to other countries i guess that should work.
Your Cisco gateway needs to be configured to recognise the country code, area code etc this way some digit stripping will occur and the call goes out as expected.