Abdio 3GP Video Converter can convert videos from almost all the popular video formats to 3GP. The program has a very user-friendly and simple interface that lets you convert any video for your iPhone or any 3GP player in three easy steps.
What may be considered a disadvantage of this converter is that the output video format cannot be changed. It is fixed to 3GP. However, the program allows you to customize the output 3GP videos: you can change the video resolution, video bitrate, audio bitrate, audio codec etc. to get the desired video quality. You can also normalize the audio of output videos using the built-in audio adjuster. The conversion speed of the program is quite good but the output video quality is strongly dependent upon the input video quality and format. This becomes especially apparent when you utilize the program's batch conversion feature.
In short, the program is a good 3GP converter with most of the required features. However, there are far better variants on the web that are available for a lower price or even for free.