Last year I squeezed some room in my camera collection for the Diana set from Urban Outfitters. I don't get as much use out of it as I would like, the film takes me at least a month to develop, so it's not too practical. I was going through my lenses today and decided it was time for an experiment.
I found that the 55mm lens worked the best for this. All you need to do is place the lens on your phone directly against the lomography lens and take away!
Normal phone camera
With 55mm Diana lens
All I can suggest is experiment with all kinds of lenses and see what works. Not every lens I had worked with the phone, even if it looked fine holding it to your eyes. It will still create light leaks and vignetting just as you were using the camera.
Isn't this little guy adorable? Tomorrow I get my newest camera, so excited!