Welcome to Android Central! That means that text messages longer than the 160 SMS character limit are being broken up into separate SMS messages, rather than being sent as one whole MMS message. MMS requires mobile data, so this can happen if your mobile data isn't on, or if your APN settings aren't set correctly. There might also be an option in the Messaging app's settings for how to send long messages (i.e., as multiple SMS messages or as one MMS message).