if you have a mp3 player you can use it, it will be better than the phones. i personally however use my SE K750i to record the classes. the quality is ok kinds. This is because my teacher uses microphone and loudspeaker. but sometimes i do not understand what is he talking. SE uses compression to restrict the size of the file. Mp3 players will record in Wav format which is not compressed.
t610 from transcend will be a good choice.