No, roaming is not free in Turkey with your European (EU) or UK SIM card because Turkey is not part of the EU's 'Roam Like at Home' zone. This is a common and costly misconception for many travelers. While Turkey is geographically located in Europe, it is definitively NOT a member of the European Union, which means your "Roam Like at Home" (RLAH) plan does not apply there.
Attempting to use your standard EU or UK SIM card for data roaming in Turkey will likely result in extremely high charges. Most major EU and UK carriers, such as Vodafone, O2, EE, and T-Mobile DE, will impose significant international roaming fees, often ranging from £2 to £6 per day, or even more per MB of data used. This can quickly lead to an unexpectedly large bill.
To avoid these expensive roaming traps and ensure you can use your data in Turkey affordably, consider a local solution. A Cellesim eSIM offers a one-time prepaid fee, providing a significantly cheaper and more predictable way to stay connected throughout your trip without the worry of hidden costs.