Just a suggestion but there is a *lot* of amateur 3gp posts out there, people take pretty hot amature shots and tend to swap from phone to phone. As yet I haven't found a site that specialises in 3GP posts of this nature.
It's often the case that people convert them to avi (often causing sync problems) and I think the converted files don't attract mobile fans as they then have to reconvert again to transfer them to the phone.
How about trialling a 3gp area ? Those users without phones can still play them using the free nokia player
http://europe.nokia.com/nokia/0,5184,5371,00.html
There really is a lot of material out there but only a few make it to torrents and with a few exceptions only the desi and pinay clips make it to websites/blogs, a respository for 3gp clips might attract mobile uploaders. What do you think ?