How to convert .3GP movies, taken with mobile phone, into .AVI ?

Convert 3gp to avi with QuickTime Alternative and Zwei-Stein Converter Download freeware Zwei-Stein Converter.

Next, download and install free 3gp codecs intended for converting files: Quicktime Alternative.

1) Launch Zwei-Stein (Click Start -> Programs -> Thugs at Bay...)
2) Press File -> Import -> Import Video Clip
3) Select type of files - "All files (*.*)"
4) Open your .3gp video clip.
5) Press File -> Export -> Video for Windows (AVI)6) Enter filename.
7) Choose video codec. DivX, XviD or WMV9 are recommended.
8) Click OK! That's all.

NOTE: You can change several parameters before conversion- Video Dimensions (menu Destination -> Video Format)- Video Frequency (menu Destination -> Frames Per Second)- Effects (menu Source -> Add Video Effect)