I got one today from the following number: +447005113859
I called it from my work landline, as I didn't want to risk calling this number from my own mobile. A recorded message answered, stating "I'm sorry, but we didn't recognise the number you are calling from. Please enter your number and press the hash key." I entered my mobile number, and got the same message.
I then realised that I'd been scammed. I've informed Orange about it, but they weren't really that helpful with the fact that I was reporting a scam to them!
I checked with BT for the charge band relating to the code 07005, which is a Personal Number under the charge band pn2. Calls to this number are charged at 50p/min at all times.
So you're getting charged 50p/min to enter your number repeatedly into an automated service that is there purely for that purpose.
The moral is: if you get a Missed Call Alert from Orange (or any provider for that matter) and you don't recognise the number, don't call it back. If it's important, they'll call you again!
(crossposted to thelovebug and livejournal_uk)