This is a secret mobile number on a PAYG SIM card.

Now this new mobile gets a phonecall once a day. CLID says "unknown" and the
odd thing is that it never activates the answerphone and rings for a full
minute before stopping. It never calls at the same time of the day but never
rings at night. It's always silent if I answer the phone.

Any ideas? I got the first phonecall within 12 hours of activating the SIM
and no-one had the telephone number at the time other than me and one other
person (I doubt she has anything to do with it)

--
Adam