Yes, but ....
Yes - you can use applications such as FaceTime to communicate (voice or video) from iPhone to iPhone (or other Mac/Apple device). Kids will most probably love to show their skills on how setting up the phone and update the telephone directory, and how to use it.
But make sure the iPhone is set to no-roaming - it's by default (after complaints following astronomical telephone bills of US users abroad). So you will have to use some other internet access for communicating - best being usually free internet access at hotels (or other W-LAN access points).
Might be worth also checking with your mobile telephone supplier on limits roaming abroad - some service providers block data roaming once a certain limit is reached. Some service providers simply do not allow data roaming, or users can ask to set limits in order to avoid excessive bills (in case of unintentionally switching data roaming on)
In case you want to avoid totally all chances for roaming bills and your provider is not helping you - get a maybe old iPhone with a prepaid SIM card in your country - load just a small amount that worst case will be used up in case of unintentional data roaming. Thats what I am using now for trips abroad (in fact an old Nokia with dual-SIM cards - one prepaid "home", one prepaid from the country I travel most of time with for both specific roaming plans). For the iPhone with postpaid contract SIM I leave data roaming off all the time (wherever I might be).
By the way: iPhone SMS is also using internet communication rather than regular SMS phone function. SMS application is blue when using iPhone SMS function - in case you have not internet connection SMS transmission will not work, users get an error message and can if they want send the SMS as regular text message - then the application is using a green background, SMS will be charged for transmitting a regular SMS.
And maybe also worth mentioning - assuming you test FaceTime at home, make sure to already use international phone number codification for your phone directory - for Australia +61 ..... - so no change required when abroad, should work also within Australia. I have all the phone numbers I use with the respective +00 whatever country code and phone number in my phone directory, so no change necessary when calling from an other country.
Edited: 6 years ago