I want to use my AT&T iPhone – specifically the data connection – while in Turkey in September.
What's the easiet, cheapest way to make my phone work in that country? How good is the service? Is it even worth it outside of Istanbul?
You probably don't want to use AT&T roaming. It does work but the Turkish providers are going to hit you up with some pretty beafy data fees. Getting a local SIM card is prefered.
Your AT&T iPhone should support GSM bands and a SIM card, but there are a couple bariers. First your phone is probalby locked -- meaning the software in the phone won't accept anything but an AT&T SIM card. You can talk to AT&T about getting them to unlock it for you so that you can use it while traveling. As long as they don't think they are going to lose you as a customer they will sometimes do that. Alternativly you can hack it yourself to get it unlocked.
Coverage in all major cities is pretty good. You can usually get pre-paid cards from any of the major operators (Turkcell, Avea, Vodafone) at the airport or at any shop. The pre-paid SIMs get a certain amount of credit, then you can use that credit to add a data package. The more data you buy the cheaper it gets per unit.
Secondly and specific to Turkey are foreign phone import issues. Your phone will work in Turkey as a "guest" for a while, but don't plan on more than a couple weeks. As part of the import restrictions, you must register the IMIE number of your phone. If you don't register your device as having been imported it will get blocked from the networks after a period of a couple weeks. Sometimes they actually do this, sometimes months later they haven't gotten around to it. If you have a residence permit you are allowed to import one phone per year free of charge, but you can't do this on a turist visa.
This is the long-term best strategy:
The Apple Online Store sells the latest-version unlocked iPhones for:
With an unlocked iPhone, you can use foreign SIM cards. And it will be inexpensive to use. However, the upfront cost is higher. An unlocked iPhone is a few hundred dollars more than one under contract.
If you're not staying abroad too long, and you don't travel abroad much else, then consider swallowing the expensive roaming fees. It may be the cheaper option then.
Considering two facts that you are mainly interested in data connection and buying a SIM Card is quite complicated for foreigners in my country, I would switch my phone to flight mode and look for mobile wifi rental options in Turkey.
So you can skip the main hassle about AT&T and other complications.