Use Freemake Video Converter for Microsoft Windows to transform H264 video files to 3GP Multimedia for wireless networks format.
Mac users can use Adapter converter for same purposes.
Also you can transform H264 files with FFmpeg command line tool with command:
ffmpeg -i /path/to/your/file.h264 -vcodec copy -acodec copy /path/to/your/newfile.3gp