While I was in Canada over the weekend, I did some experiments on not having the Minternational pass (too expensive to consider using). I found that in order for WiFi calling to work, I had to try to make a call on the Mint line, I would get intercepted to a recording claiming to be the Mint Fox which was going to transfer me to buy a pass. I hung up. WiFi calling woud then work for a while. If I changed WiFi networks or went too long without some form of activity, the WiFi calling would drop. When WiFi calling is working SMS can be sent and received. MMS on WiFi for Mint has never worked for me.