According to AppleInsider the USPTO filing describes an interface similar to the existing SMS (Short Messaging Service) text messaging interface for the iPhone, but with key changes.
In normal use, users would continue to use the same bubble chat interface as with today's phone, complete with the ability to start new messages by searching through the contact list or typing the first few letters of someone's name. Users can also see a past chat history and remove individual conversations from the list.
However, the patent also adds features not present in the current iPhone software. While one chat view closely resembles that of the current SMS interface with a dedicated text field for entering new messages, another would have typed text appear directly in a new message bubble and would replace the text entry box with a list of suggested words.
Source: AppleInsider (Patents alternate version is on the right)