Yes, you can use the wifi with just a password, and Skype and iMessage will work. You might want to use What’sApp also, because it works via wifi. If you want to make sure you don’t incur unintended cell usage, put your phone in airplane mode while in Austria and Germany. You can always turn it on momentarily if needed. You will need a plug adapter. Check with Apple on the voltage converter. Better to take the time to check now than to fry your phone.