In the Spanish bomb attacks, mobile phones were used as detonator timers. But they were activated by the phones' alarm mechanisms, and one was accidentally set to the wrong time. When it did go off, it failed to detonate the bomb to which it was attached, providing investigators with a clue that led, ultimately, to Mr Rabei's arrest.
http://www.guardian.co.uk/international/story/0,3604,1235263,00.html
The SMS system outlined in the Italian arrest warrant would allegedly have got around that key weakness in the Madrid bombers' plot.

Police in Milan arrested a man Italian officials now identify as Hamed Sayed Osman Rabei on Monday. The 33-year-old man, also known as Mohammed the Egyptian, is suspected of playing a leading role in the Madrid train bombings and is wanted by the Spanish judicial authorities.

The 27-page Italian arrest warrant also includes an extract from a transcribed conversation in which Mr Rabei allegedly boasted of knowing a method that allowed him to change his fingerprints.

"They are never the same. Not even the American intelligence services will find me. So, you will see that today I have some fingerprints and tomorrow others," he is allegedly quoted as saying.