Messages may be sending as SMS instead of iMessage for several reasons. The most common is that iMessage requires an internet connection. If the iPhone cannot connect to the internet or the recipient's device is not available or does not support iMessage, the message automatically falls back to SMS using the cellular network. This happens when:
- Either sender or receiver does not have iMessage turned on or available.
- The recipient uses a non-Apple device (e.g., Android).
- Network or internet issues temporarily prevent iMessage delivery.
- The "Send as SMS" option is enabled, allowing fallback to SMS if iMessage fails to send.
- The recipient has switched devices or turned off iMessage.
To prevent messages from sending as SMS, you can toggle off "Send as SMS" in your iPhone's Settings > Messages. Note that this will stop automatic fallback but won't affect sending to non-iMessage users, which always goes via SMS. In summary, messages send as SMS when iMessage is unavailable on either end or connectivity is lacking, with an option to disable fallback via settings.
