On 26 June 2003, I had my head shaved and then put into an iron "halo" to hold it still while I had an MRI scan, which the surgeon used to navigate the electrodes.

CNN: 'I had brain surgery while I was awake'

But things have since changed, with that figure rising to 13 in December 2003, 26 in December 2004, and 38 in June 2005, the most recent date for which figures are available from the Cellular Telecommunications Industry Association, an industry body.

ECONOMIST: Text messaging