Regular internet access as you travel through Turkey is a problematic proposition.
Public wifi in cafés, tea houses, restaurants and malls are virus and Trojan-laden danger zones. There aren't decent prepaid mobile internet access plans. The whole cell phone thing is overburdened with a government eagerly trying to register every single mobile device and user. There are entirely too many obstacles to practical solutions.
It looks like a small, but very efficient operation in İstanbul is trying to change that. I had a chance to try out Alldaywifi, and , I can confirm that it works just as advertised.
For $5 a day, you get a small device and an extra battery. I did not have the time to examine the technical details, but, as I understand it the device connects to the internet using a 3G modem, and creates a local WiFi network. You don't get admin access to the WiFi configuration, but you do get a sufficiently generic looking name along with a password that is different than the WiFi network name.
Once the modem is connected, all your devices can have internet access by joining the local WiFi network. In my experience, the connection worked reliably in a number of rural towns, along desolate highways, on mountain tops, etc, and maintained a decent connection at various speeds and weather conditions.
Don't assume this makes you safe from every type of attack, but it is much better than relying on open networks in public locations.
Of course, this is too expensive for a long term solution: There are monthly internet plans for less than two days of alldaywifi, so if you are going to be staying for the long haul, definitely look into getting one of those.
I had a chance to talk with Erinç (one of the co-founders), and Karin (operations manager) on a couple of different occasions, and they are some of the friendliest, most customer-service oriented, polite, and practical people you can find in Turkey. Their service is a breath of fresh air.
They were not too impressed with a tech blog, so I did not get any special treatment or discount in exchange for this review (I did ask), but if you do have a travel blog, and you are traveling to Turkey, do get in touch with them, and see what they can do for you.
If you are a developer who needs reliable internet access for a short visit to Turkey, alldaywifi does present a viable alternative. Just grab a low cost VPS, and set up OpenVPN with TLS, and use it over alldaywifi's connection instead of sharing public WiFi, and being chained to specific locations. It is not blazing fast, but even Windows RDP worked well enough for me.
My brief, but satisfying, experience with alldaywifi saved me time and hassle. I would definitely use the service again.