[kuba.g]

I used MásMovil in Spain, which is probably not the best choice from the tariffs point of view (they have a minimum charge of €1 each month, for example).
But I can tell you something about the registration procedure: it is strictly necessary (by law), although sim cards bought from unofficial vendors can be used for a limited time (I thought 1-2 days, correct me if I'm wrong) in which you are supposed to register your sim card by posting the registration form to MásMovil. I bought my card from an official MásMovil dealer and it was activated within 15 minutes. No need for an address/social security number in Spain.