This one was annoying, and I don't yet know if I will run into a registration problem. This is a different registration than France, which registers the SIM. In Turkey they register the phone. We ended up paying TL70 for a Vodaphone SIM, and then applying the TL50 credit towards data. The TL20 balance is for the SIM. Voda offers 1 gig for TL21 and 4 gig for TL39. The balance of the credit - TL11 or TL29 respectively - goes the phone time and. SMS.
TL70 is around US$40.
For a mere TL4 we could have bought cheaper international calling. I skipped that, as I use an app called Talkatone which lets me initiate and receive calls to and from the US for free by using my Google Voice number, including free calls to my fellow travelers on this trip to their Google voice numbers. Funny to call the States and have it ring next to you while wandering around Cappadocia! If I were a European traveler, this option would have been useful.
All three carriers are in the airport. I first went to Vodafone, and they quoted me TL110 ($60). I went to Turkcell and got a quote of TL70 plus TL24 for the 1 gig data package. (In retrospect this deal may have been ok but broken English made it hard to discern if the TL70 had a credit to be applied to the data plan and the extra TL24 was confusion.) I then went to Avea and got a third quote of TL55, the best deal of the bunch.
Problem was, my technically astute daughter had also queried the Voda store. They wouldn't deal with her - a woman !? - so I came by and got a quote of TL100. Two different quotes from the same shop. Are we in a Turkish bazaar? Rather than find out we quit the airport and searched for the SIM elsewhere. The impression we got - and it may be erroneous - is the airport vendors rip off tourists.
We found one in a business area. Actually all three - in a mall near our hotel. We got no quote from Avea due to lack of English and got a quote from Turkcell of TL45 for the SIM and TL 25 for the data plan. In the end we chose Voda due to better language skills, and did the TL70 deal discussed above. I am not sure we couldn't have found a better deal - say, a tablet only data plan that would work in our phones - but didn't want to continue to struggle with language and time.
As to registration, both Voda and Turkcell assured me that IMEI registration is not necessary for a short-term tourist. Turkey requires phones brought into the country to be registered. Online stories vary as to what happens without registration - sometimes the service is just turned off in a few days. I guess we'll find out. We are here a week.