iOS 17.4 is now available for supported iPhones and this brings SMS support on VoWiFi for Spark.

Is there any chance that devices that support vowifi but aren't on their compatibility list might still work?

gzt: There is always a small chance. Do you have a particular device in mind?

My Dad's Xiaomi poco x3 pro in this case. Might check if there's the option to turn it on next time I get a hold of it. Would solve a lot of problems for him.