Well, it supports any file which is supported by your phone. I'm not quite sure what kind of files are supported by the K750i. But .avi is not a "real" filetype. It could be encoded with divx, xvid or many other codecs.
The W810 should run the program perfectly, K750i is partially supported. Unfortunately I don't know what the developers mean with "partially" and can't test it right now, because I sold my last DCU-60 cable and won't get new ones until monday.