Personally I don't think I'd care if it was a 10 second delay. (It often takes me that long to find the right key to open the door.)

edit: One international issue that has occured to me is the cost of texting a foreign number. Do you have any idea of how many users you'd want to have from a country in order to get a number that's local to them? (And/or is your SMS provider unable to do that?)