You can buy on eBay a router (search for 3G hotspot) that can be used with a 3G sim/dongle (available from any of the mobile shops in Calis). I have seen some where you can insert the sim straight into the router and others where the sim sits in the dongle and you plug the dongle into the router.
This then creates a wireless network where you can then connect any device to it, and in turn the Internet (so it will work with iPhones, iPads, computers etc etc)
It's a little bit of upfront cost (c£30 for the router and then the cost of the sim/dongle in turkey - though you might be able to buy a cheap unlocked dongle on eBay as well), after that though it can be reused at a pretty low data top up cost for any visit. Plus you could share the connection with close neighbours