Hi @Murray Finlayson, 

Thanks for reaching out about this! You are correct - double opt-in is set at the list level. If a list has double opt-in, everyone who subscribes to that list must confirm their interest before they're added. The only exception is for SMS subscribers in Australia and in the UK when you're using branded sending IDs. Double opt-in is enabled at the list level so if a list has double opt-in enabled, it applies to both email and sms. It isn't possible to turn it off for email and enable it for SMS, and vice versa. Switching to single opt-in will apply to both email and sms. Let me know if you have any other questions about this! 

~Chloe