It is Simple to create high quality 3gp video .

Adjust setting of Xilisoft according to mention as under.
1;video size :176×144 or whatever screen size u have
2 bitrate :96kb/sec
3 framerate: 13.43 fps
for the sound of the movie u’ll have to try increase or decrease the values to decrease the size or increase the quality
-Channels 1[this if u have a mono speaker on ur phone.if u have stereo sound u can easily choose 2 channel]
-Bitrate 12kbits/s
-Samplerate 8000Hz