I use an Olympus digital recorder on a tripod. Expensive , but very, very clear.
I have not used one, but you can write with a Livescribe pen that also records and will go back to the place in your notes if you need to listen to that particular part of the lecture. Link here:
http://www.livescribe.com/en-us/
The phone idea means you need a small tripod (and permission), unless you want to sit there in class with your hand in the air for an hour or more.
You can also change the way you take notes. Some find that writing in a tree diagram (think MindMapping) works well for them. You do not need to recall EVERYTHING do you? Gadgets are cool, but cost money.
Check out Moleskine notebooks. Recently they are introducing a version that works with Evernote (checked- does not seem available yet), so you will be able to take a photo of your notes and make a digital, searchable database. This works really well.
Can you borrow before you buy something? One thing is clear from all this advice: different things work for different people. You need to find what works just for you, hopefully before you spend money.