I really like learning new words but i think that it is very hard to do without lots of practice.
Are you still working on this concept? If you are and you make an english version, I think I would be interested.
Like i told another poster, interesting games that are fun might work very well.
I don't have a smartphone, but if you do, you might check out that one I mentioned. Like I said, it is called bigwords spacegame or something like that.
I was able to play it on my friends phone a little and it might be a good way to learn a few words.
I have listened to some vocab lessons on mp3 but found it kinda hard to pay attention. Without something to look at I was easily distracted.