Apple insulates us from most of the peculiarities of the cellular world’s text messaging system, SMS (Short Messaging Service), and the multimedia version, MMS. If everyone you text with uses an iPhone, iPad, Mac, or Apple Watch, you see nice blue bubbles and it’s all handled within Apple’s iMessage system. Even if you’re using SMS or MMS—where messages appear in green—Apple still hides the complexity, packaging it within the Messages app on various platforms. But you might be perplexed in one specific case, as one reader was: they use group messaging without all Apple ecosystem participants a…