How prevalent is wifi in istanbul?

I'm trying to decide if I should get some sort of miff personal 3g thing to bring with me when in Istanbul. Would this be worthwhile or is Istanbul like some other european cities where there is unsecured public wifi all over the city. I mostly just want if to be able to find my way around using my wifi only ipad. Any advice? I have a gps receiver for my ipad, but for the price of apps with downloadable maps that don't require wifi, I thought maybe I should just get a 3g wireless router so I could use any navigation app.