Yes you will be charged  for SMS/text messages as wifi is for data only. The wifi calling option still charges roaming with Koodo. Incoming texts are always free though. And any messaging apps that use data, such as whatsapp, Viber, Fb Messenger, etc, will not charge you so long as you’re on wifi. I would only add “international voice roaming” to your self-serve if you just want to be able to send and receive texts, as well as turn off data roaming in your settings.  Keep in mind outgoing SMS is 60 cents each or you pay for easyroam.