If you're using UKNP 27.0 with CallManager 4.X then beware that this may give strange behaviour...
This Dial Plan was released primarily to add 075xx mobile numbers to the list of supported E.164 numbers of the dial plan; but has unfortunately exhibited strange issues with dialling out.
If you experience issues with ISDN Q.931 messages being returned on the gateway with either "No bearer channel available" or "Number not obtainable" then you may find that the dial plan is causing the gateway to send out incorrectly formatted Plan and Type fields. This can be remedied in two ways:
1) Change the "Called Party IE Number Type", "Calling Party IE Number Type" and both Plans under the Outbound Calls settings section of Gateway configuration page of CallManager to "Unknown" instead of "Cisco CallManager".
2) Add the following line to the serial0/0/0:15 interface:
isdn map .* plan unknown type unknown
As far as i'm aware, this patch has now been recalled and Cisco are working on a replacement.