Mobile SIM cards now require registration

If you own a pay as you go SIM card in your mobile phone then you will have to register your name and address with your network provider or lose your number.  The law on mobile phones in Spain, which applies to Tenerife, says that any mobile phone numbers that have not been registered with their provider will be deactivated by November 2009, but many mobile operators are likely to set earlier deadlines.

Therefore, when you purchase a new SIM card, ensure you have your passport / certificado de registro with you.