I used the included Voice Recorder to record all of my lectures. My ONLY complaint was that it took forever to find an app that would play them on my PC at home. They are out there, though.
Also, I found out the hard way that if you turn on the camera to take a photo of the whiteboard, it shuts OFF the voice recorder and you have to remember to turn it back on. Make sure you sit at the front of the class. You'll miss comments and questions from other students, though.
Finally, I highly recommend you also take notes on the phone but don't sweat the details in class. Swype makes it a heckuva lot easier. Later, these notes make your review of the recordings a LOT faster because a lot of the notes will already be done.
Typically, I recorded lectures while simultaneously taking notes on the phone. Then went home and uploaded the notes and recordings to my laptop. I opened the notes up on screen while listening to the recordings and updated the notes in various places with greater detail.
Immensely useful. Don't make the mistake of relying solely on the voice recordings. If you do, you'll likely fail the tests.
--Wag--