[Chrisdee]

Perhaps your friend was referring to this article in the Coast Rider this week, it only applies to "Pay as you go".

If you own a pay as you go or prepaid Spanish mobile phone you could lose your mobile number and have to re-register your phone again. In an attempt to prevent terrorists and criminals using anonymous prepaid mobile phones for communication, the Spanish government has issued a decree that any un-registered phones will be disconnected on the 1st of October.
To comply with the new registration law, pay as you go users have to verify their present address through a recent copy of the padron and a copy of their passport. If you presented both those documents at the time of purchasing your prepaid phone as most people will have done, then no further action is required. However a number of mobile phone users may have just bought a SIM card to put into an unlocked handset. Until recently it was not necessary to provide proof of address for prepaid SIM cards. Any phone number that is not correctly registered on the 1st of October will be switched of. It is believed that a grace period will exist before the telephone numbers are recycled. This is likely to effect residents that are currently out of the country and will not be returning until winter.
The move has sparked debate as to the merits of such a scheme. The idea for a register of mobile phones in Ireland was extensively reviewed by officials in the respective department. There were many complex legal, technical, data protection and practical issues to be considered. In theory, a register of mobile phones might seem like a good idea. However, once they looked at the situation in other administrations, considered the ease with which an unregistered foreign or stolen SIM card can be used and having consulted with the Office of the Attorney General and other interested parties, it was concluded that the proposal would be of limited benefit, in that it would not solve the illegal and inappropriate use of prepaid mobile phones and was not practical. One can only assume that similar issues would exist in Spain.