Mixing Successfully For Ringtones Options

[crazyoval]

hi guys, Im looking for a source of advice and considerations for producing and mixing tunes / loops for creating ringtones. I want to make sure that I understand the considerations of different mobile phones and the sound issues around the frequency spectrum that is available.

Does anyone know of any good sources on the Internet. Ive looked but not come up with anything that is well focused yet.

thanks in advance