I read online that Google Voice will record incoming calls (only :/) for free.
Here's one a physical recorder I read about online:
http://www.amazon.com/Recorder-Conve...mUvbUpU2724172
Although I don't know how good it is. I think buying a physical one would save you money over time, and last for phones in the future! (However the one I linked hooks through the headphone jack, and possibly iphone 7 won't include a headphone jack so maybe a bluetooth one would be good if you're hoping to make an investment for future phones.)