I've found that although I used to be able to do it (through t-mobile) I no longer can, I also found out that it was luck that I was able to do it at all. Most, if not all, cellular providers filter all mail sent through their servers for certain file extensions (mp3 gif jpg mp4 bmp etc.) and disallows some of those file types at their decresion. But for the cost of a few ringtones you can buy a cable and make your own.

Help me out yall