What is SMS messaging on iPhone?
SMS messages are standard text messages and appear as green bubbles on iPhone.
If you're unsure as to whether your messages are iMessages or SMS messages, the colour of the text bubble can give you insight into what type of message it is.
SMS messages, when sent through your mobile carrier’s network on iPhone, will appear as the green bubble messages. SMS messages use your cellular plan for sending and receiving text messages.
iMessages on the other hand, appear as blue bubbles and use Wi-Fi or Data.