nospam,
It's generally prudent to check the chargers or power adapters of each device you'll be travelling with to determine the Input Voltage ratings. If the ratings state "Input 100-240 VAC", the products will work fine in Europe with just an inexpensive Plug Adapter such as THIS model. These are available from various retailers including travel stores, Radio Shack, WalMart, Target or other stores. It's a good idea to pack along at least two as they're small and easy to misplace.
As someone else suggested, you could also pack along a USB Charger that handles multiple devices, so you can charge all the phones at once from a single outlet. THIS product is one device that can be used for that.
I assume you've checked to ensure your cell phones will operate in Europe, and checked with your home cell network to determine the costs for that?
Your iPhone chargers will be designed for multi-voltage operation, and I assume the Samsung will be the same. The flat iron is a different matter, and you should definitely check the Input Voltage label on that. If the flat iron is only designed for operation on 115 VAC, it can be used with a Voltage Converter but that's not advisable. It should also be noted that some manufacturers of flat irons specifically prohibit use of their devices with Voltage Converters (I believe Chi is one of the brands).
I'd suggest leaving the flat iron at home and either buy one in Europe or just dispense with it completely during the holiday.