I want to make a ringtones site with the functionalities of zedge.net, I think its made up of some cms, if there is a theme or extension, add ins etc that will make my life easy.
Even if not all functionalities, I would be definitely happy with limited ones like ringtones with the functionality of ringtones management upload and download stuff. SMS notifications if possible etc.
Any suggestions on how can I achieve this quickly is greatly appreciated.
There is no best CMS, it has more to do with you than your product choice. The CMS you are most familiar with is usually the best one for the job. I prefer Joomla so I can tell you that I would do the site you mentioned using a combination of Joomla, K2, JomSocial, and a couple of other extensions to achieve the same basic type site. I am sure that you could do the exact same thing with Drupal, Plone, Wordpress, or DotNetNuke.
If you don't have a preference then take a look at the popular options and see which one fits your needs the best. Check out the communities, the extension libraries, and the framework they use then pick the one that sounds the best to you.