To power your iPhone 3GS from the Croatian power outlet you'll need to buy a Type F USB power adapter  and USB to Apple 30 pin cable  (normally supplynig with iPhone 3GS by Apple).
To power your iPhone 3GS from the Croatian power outlet you'll need to buy a Type F USB power adapter  and a USB to Apple 30 pin cable  (normally supplied with the iPhone 3GS by Apple).