ToneThis is a program to do all this and more, all aimed at customizing your mobile phone.
The program has four main options: creating ringtones, wallpapers, videos, and games (although the latter option is not available yet).
To convert any song, video or image saved on your computer to the appropriate format, you just load the appropriate file to export later. ToneThis doesn't save it directly to your computer, but rather gives you a direct download link that expires in one day.
The program supports approximately 300 mobile phone models, covering all the most popular manufacturers (LG, Motorola, Nokia, Samsung, SonyEricsson, etc.).