Well, most types appear to work. I've tested .mp3, .mp4, .m4a, and .m4v with success. **Edit: it appears that GSM .wav file are supported). ** Still not supporting all .wav formats/encodings (probably not .avi or .wmv). So if you are limited in space and have wifi, you could use Gmail to store vids/audio. Greg p.s. I tested my Vonage vMail and it does not play.