Is there an iPhone app that will save all SMS msgs from a certain user to a text or image file?

I have a HUGE textversation I need saved to be used elsewhere and it is way too long to screenshot and it will take a long time to transcript. I know there are programs that will read your backups and extract the SMS conversations but they aren't very good. Is there an app that will just save the conversation? I've looked and haven't had any luck.