You can register your phone, but you have to pay 100TL (Turkish Lira). This rule has just begun like a month ago. before, it was only like 10TL.

People brought many (illegal) phones from outside turkey, so they've made the registering much expensiver...

Glad i've registered mine JUST BEFORE the rule went alive

By the way, you only have to register if you want to use a Turkish local simcard. (Turkcell, Vodafone, Avea. I prefer Vodafone!)