Unfortunately sending messages is not available for any Apple device using cable communication. iOS is a restricted system and this is a limitation by the manufacturer.
However we have developed a solution which will allow you to send messages using iPhone. Connect your phone using Wi-Fi (MOBILedit for iPhone must be installed on the device) and send your message using MOBILedit. The text message you write in MOBILedit will be shown on iPhone screen when you hit Send.