Hi needforinfo,
If you are sending messages between iPhones, Messages will use either text messaging (SMS/MMS) or iMessage, depending on what is available and what kind of connection can be made at the moment. You may find the following article helpful:
How do I know if I am sending an SMS, MMS, or iMessage?
The type of message you are sending is noted by the color of the send button and text bubble.
- A text message sent as SMS or MMS will show the word "Send" in green when typing and have a green text bubble.
- A text message sent as iMessage will show the word "Send" in blue when typing and have a blue text bubble.
Some carriers may automatically convert long SMS messages (ones that would require multiple SMS messages to send) into MMS format.
On iPhone, if iMessage is unavailable, the message may be sent as SMS or MMS, depending on the content. Carrier messaging rates may apply. You can adjust this behavior on your iPhone at Settings > Messages > Send As SMS.
iOS: Using Messages
http://support.apple.com/kb/ht3529
Regards,
- Brenden