Messages is the iPhone's text messaging application. Messages comes preinstalled on all iPhones, and you cannot delete this application from your device. Your iPhone will automatically store all incoming and sent text messages within the Messages application indefinitely. You can, however, choose to manually delete messages from this application.
Accessing Text Messages
Tap the "Messages" icon from the home screen of your iPhone to access your stored text messages. The application will display all text messages sent and received in chronological order. Tap a text message to display the entire text message thread. All text messages sent to and received from the same contact will appear in a single text message thread.
Delete Text Message
To manually delete a text message, tap the "Edit" button from the summary screen of the Messages application. Once you tap "Edit," you will see red circles displayed to the left of every text message. Tap a red circle to delete the individual text message. Tap the "Delete" button to confirm. Once you delete a text message from your iPhone, you cannot recover the message.
Send Text Message
To send a new text message, tap the "New" icon in the upper-right corner of the Messages application. Start to enter a contact name in the "To" field to send a text message to one of your contacts. Select that contact from the list of available contacts. Alternatively, you can input a cellular phone number to send a text message to someone besides one of your iPhone contacts. Enter the text message you want to send and tap the "Send" button to send the text message.
Your iPhone also allows you to send MMS messages from the Messages application. After tapping the icon to send a new text message and entering a contact in the "To" field, tap the photo icon to the left of the field where you would normally input your text message. Select the iPhone file you want to send and tap the "Send" button. You can send photos, videos, music files and several other types of digital media using the MMS feature of the Messages application.