Machan i have the same phone, but to the best of my knwledge i dont think a nokia 6120c iz having the capability to play such a file because an avi file has more resolution and more sound quality, the advice i can give you is that its better if you get a convertor to get your avi file converted... heres the smallest and the most easiest converter i have heard of,
http://youtubedownload.altervista.org/
this is a bundle of a software that you can use to download youtube files AND convert any type of files....Once you install and run the program, select the option "convert video previously downloaded" and then select the file and on the drop down menu select the type of file to be converted as "3gp" because this is definieately supported......you can choose the quality and then once you convert, the converted files are on the same destination as your ".avi" file path....

....If you want an advanced converter download this torrent...
http://www.mininova.org/tor/2669631
This program is really worth it to any type of video convertions...


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Enjoy and send me the "pin" ok..


...Lolzz..
Also checkout my video works that ill make you laugh your ass of...XD
www.youtube.com/ludamycentral



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tell me how it was k?