Each time I try to start a conversation with someone NOT using an iPhone, it tries to send them an iMessage. It gives me an error saying this number isn't activated for iMessage, and fails. If I start the conversation from my PHONE first, it syncs fine, and I can continue to participate in the conversation. Why can't I start an SMS conversation from iMessage on my mac? Why is it always trying to iMessage people who don't even have iPhones?