I only know one way!! But on the back of magazines or near the back you will probably find a page with loads of different advertisement's, look for music part and there will be all the latest songs on it, the instructions will be on the page, once you have finished texting it to them you will receive a text back explaining what to do. That way you can download as much music as you want!! Although it does cost £3 pounds!! You can also download lots of wallpapers and games etc.
Hope this helped!