UK Mobile Phone

Vodafone UK allows all their packages to be used in Turkey with no additional charge.
For less than £16 a month you can have unlimited calls and texts ( including incoming calls and calls to Turkish numbers whilst in Turkey ) free.
This package also includes 100 Gb of data per month which can be used in Turkey.
You can easily create a WiFi hotspot with your phone to share your data with other WiFi equipment ie IPad.
Your UK phone does not have to be registered in Turkey as you are not using a Turkish phone provider.