first off all download unlocker and after download install on pc and then after which file u went convert left click on the file and click on unlocker option and then select rename and after that u see file name for example funny.3g

p an d rename this fito funny.avi and thats it the file convert from 3gp to avi the download link of unlocker is http://download1us.softpedia.com/dl/729bd1c5372db4608b01a5da99b5f64e/4ddc9e6f/100068439/software/system/Unlocker1.9.1.exe