'Ya tengo lo que me pediste. ¿Cuando te lo doy?' (I've got what you asked me for.  When shall I give it to you?) - trick SMS like this one from four-digit numbers are becoming more and more frequent.

Just by answering, for example: 'No sé de qué me hablas. ¿Quien eres?' (I don't know what you are talking about. Who are you?) will activate an account with a premium-rate mobile 'phone information service and that response alone could cost the mobile 'phone user 1.50 euros, rather than the 15 cents for a normal SMS.

According to Enrique García, a spokesperson for the consumers' association OCU, 'by replying to the four-digit number you are effectively accepting their services and will start to receive messages from them from that will cost you 35 cents, whether you open them or not'. 

'What these companies want,' Garciá said, 'is for people to reply and then they are hooked into a receiving premium alerts'.

Mobile 'phone users could receive several premium messages per day with songs, videos, games, newsflashes etc, racking up a tasty bill for the 'service provider'.
 
The office of data protection has received 63 complaints about 'spam' messages from these four-digit numbers since 2007 and 33 investigations have resulted in seven successful prosecutions, but many of the investigations have led to nothing since the 'service providers' are registered outside of Spain.

At the instigation of the consumer's association, a new code has now been drawn up, obliging these services to make their tariffs clear to the consumer and making it impossible to get drawn into the 'service' without sending the word 'ALTA' back to the four-digit number.  Cancelling the 'service' will also be a straightforward case of sending back the word 'BAJA'.

It is yet to come into effect, so the current advice from consumer associations is not to reply to unsolicited messages from four-digit numbers, i.e. not to enter into the game.