According to AppleInsider the patent filing contains descriptions for sending text messages, e-mails, contacts, documents and more to a caller while two phones have established a voice connection.
In the patent entitled, "Auto Messaging to Currently Connected Caller", Apple explains the current situation...
"While a user of a mobile device is using telephony services, the user may want to send a message or a file to another part. To send this information, the user may have to disconnect the call, and then perform a lookup of the caller's contact information prior to being able to send the message or file. This multi-step process can be tedious for the user."
Apple's solution involves a user interface that provides messaging capabilities while on a call. It would automatically detect the callers' details and send the information accordingly.