Thaivisa is running an item about the ‘Mandatory registration of SIM cards in Thailand’.
http://tech.thaivisa.com/sim-card-registration-thailand-update/3112/?utm_source=newsletter-20150122-1454&utm_medium=email&utm_campaign=news
There was a thread back in 2005 about this:
http://www.pattayatalk.com/forums/topic/14538-ids-to-be-mandatory-for-sim-cards/
When I first got my TrueMove SIM (about four years back) there was no mention of ‘registration’, but when I upgraded to 3G in BKK last year I was asked to show my passport, although, as I recall, a photocopy was OK. I was