Data protection act - Data must not be disclosed to other parties without the consent of the individual whom it is about, unless there is legislation or other overriding legitimate reason to share the information (for example, the prevention or detection of crime). It is an offence for Other Parties to obtain this personal data without authorisation.
I suspect any legal case would hinge on whether your mobile phone number counted as personal data or not. Again, IANAL, but the Data Protection Act is not specific on what counts as personal data and instead leaves it up to case law and I think the data registrar(?) to clarify.
On the other hand, in some contexts we hand our numbers out freely :-) I may be being pessimistic, but I suspect lawyers would have expensive "fun" with the details of this one.
