Any image you've got can become a wallpaper! All you need is to resize the image to a size that matches a device. Photoshop is often used but if you cannot buy it, try using PicResize.com for free.
Themes make your phone look incredible and allow for full customization. Go grab the BlackBerry Theme Studio and start sharing those themes!
Ringtones are made quickly with online converters. Check out MakeOwnRingtone.com for an awesome and free converter that requires no registration!