How do I view videos on my computer which I took using my phone (3gp files)?

Moreover, it allows users to select DVD subtitle and audio track to convert DVD movies of any available languages, as well as trimming favorite parts and cropping DVD. This smart DVD Ripper for Mac also allows users to split DVD movie to different chapters.it can be used like iPhone video converter, 3GP video converter, PSP video converter, iPod video converter, and Zune video converter to convert any video format to your mobile phone, Sony PSP, iPod, Apple iPhone, Zune video player and other portable video players.
so you can free download it from here

HD video converter for mac helps you to convert HD Video to Mac OS X 10.6 Snow leopardiPod

It supports so many devices and video formats, such as: iPod, iPhone, PSP, Zune, Xbox, Nokia, avi, wmv, 3gp, mov, flv and more into avi, mov, asf, wmv, mp4, 3gp and others.
Altysoft Video Converter is a very easy and powerful DVD ripping software, which can convert DVD to various formats.

MOD converter is a powerful JVC camcorder Mod format video converter which can easily convert .MOD to other popular video formats.

Altysoft Video Converter can help copy whole DVD to your hard diver, then you can burn them to blank DVD using burning software.
Beside above-mentioned functions, it so easy to download YouTube videos from YouTube website, just specify the URL for the video you want to download.
You should change another video converter. You can use iSkysoft Video Converter. It can convert WMV to MPEG, AVI to MPEG, WMV to MPEG etc. and supports video formats including MP4, MOV, 3GP, AVI, WMV, RM, MPEG, ASF etc., and audio formats including MP3 WAV, WMA, AAC, AC3, OGG, APE, M4A, etc.

Specializing in formats meant for portable devices, FLV Converter also supports.

maybe you should try the uSeesoft Total Video Converter
Inputs: WMV, WMA, AVI, MPG, MPEG, RMVB, RM, RA, MOV, QT, MP4, M4V, DV, DAT, MP3, AAC, etc.
Outputs: 3GP, 3G2, MP3, AAC, WAV, M4A, etc.
It is free with no limitation and easy to use. You can have a try, and here are some steps.
1,open the program, click add to find the video you want to convert.
2,setting. choose the mp4 as output format, and the folder you want to save your mp4 video in.
3,click start then wait till the process finished.
4,when you got the mp4 video, you can drag and drop it into the video folder in your mp4 player.
And I think this guide may can help you too.