Just look at the status bar of your at the top of your i Phone.
In both situations it is key to not text using SMS (green texts), however if the i Message cannot be sent it will attempt to send using SMS by default.
You can disable this feature while abroad to avoid charges.
Today we go everywhere with our phones and traveling without them is not an option.
However, data roaming fees, excessive charges for texts and calls can lead to many people turning off their phone and leaving in in the room.
i Message is part of any i Phone with i OS 6, 7, and 8 so most people will already have it.