My experience with Turkcell ended in June 2012:
http://yachtvigdis.wordpress.com/mob...ess-in-turkey/
In that blogpost is a link to the Turkish site which is supposed to give the latest regulations:
http://imei.tk.gov.tr/
Note that the English version of that site is out of date: you'll just have to use google translate. And in Turkey (and throughout the Med) there is often a big difference between the law and what actually happens.
The 2013 regulation on the istanbulletin site (nice name!) looks very plausible to me but I've no first- or second-hand knowledge of it. Please feedback your experience.