The Accidental Charges
By default, the iPhone attempts to ensure your messages are always delivered. If you send an iMessage (the blue bubbles) to another Apple user, but your cellular data connection is incredibly weak or drops entirely, iOS will automatically convert the message into a standard SMS text message (a green bubble) and send it over the cellular voice network. While this guarantees delivery, it can be extremely costly. If you are traveling internationally without a roaming plan, a failed iMessage automatically converting to a green SMS bubble can result in massive, unexpected cellular carrier charges. You must force the iPhone to only use data for iMessages.
How to Turn Off Send as SMS
You can permanently block the automatic fallback feature via the Messages settings.
- Open the Settings app on your iPhone.
- Scroll down the main list and tap on Messages.
- Look for the toggle switch labeled Send as SMS (usually located right below the main iMessage toggle).
- Toggle this switch to the Off position (the green background will disappear).
Data Only
The change takes effect instantly. The iPhone will completely sever the automatic conversion engine. If you attempt to send an iMessage and your data connection fails, the message will simply sit in your outbox with a red “Not Delivered” warning. It will never automatically fall back to the cellular text network, guaranteeing that you will never accidentally incur international SMS charges. (Note: You can still manually send regular green text messages to Android users; this setting only applies to failed iMessages).