Here the results of my tests:

1) ffplay test
==> the video is displayed correctly, but I can't hear any sound
==> the output of ffplay command is:
###############################################
nicola@nicola-laptop:~$ ffplay '/home/nicola/Video/Miei/Telefono/VIDEO0003.3gp' FFplay version SVN-r0.5.1-4:0.5.1-1ubuntu1, Copyright (c) 2003-2009 Fabrice Bellard, et al.
  configuration: --extra-version=4:0.5.1-1ubuntu1 --prefix=/usr --enable-avfilter --enable-avfilter-lavf --enable-vdpau --enable-bzlib --enable-libgsm --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libvorbis --enable-pthreads --enable-zlib --disable-stripping --disable-vhook --enable-runtime-cpudetect --enable-gpl --enable-postproc --enable-swscale --enable-x11grab --enable-libdc1394 --enable-shared --disable-static
  libavutil     49.15. 0 / 49.15. 0
  libavcodec    52.20. 1 / 52.20. 1
  libavformat   52.31. 0 / 52.31. 0
  libavdevice   52. 1. 0 / 52. 1. 0
  libavfilter    0. 4. 0 /  0. 4. 0
  libswscale     0. 7. 1 /  0. 7. 1
  libpostproc   51. 2. 0 / 51. 2. 0
  built on Mar  4 2010 12:41:55, gcc: 4.4.3
nicola@nicola-laptop:~$ 
###############################################

2) melt test
==> the video is displayed correctly, but I can't hear any sound
==> the output of melt command is:
###############################################
nicola@nicola-laptop:~$ melt '/home/nicola/Video/Miei/Telefono/VIDEO0003.3gp' 
+-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+
|1=-10| |2= -5| |3= -2| |4= -1| |5=  0| |6=  1| |7=  2| |8=  5| |9= 10|
+-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+
+---------------------------------------------------------------------+
|               H = back 1 minute,  L = forward 1 minute              |
|                 h = previous frame,  l = next frame                 |
|           g = start of clip, j = next clip, k = previous clip       |
|                0 = restart, q = quit, space = play                  |
+---------------------------------------------------------------------+
Current Position:        367
nicola@nicola-laptop:~$ 
###############################################


3) ffmpeg -i info
==> the output of ffmpeg command is:
###############################################
nicola@nicola-laptop:~$ ffmpeg -i '/home/nicola/Video/Miei/Telefono/VIDEO0003.3gp' 
FFmpeg version SVN-r0.5.1-4:0.5.1-1ubuntu1, Copyright (c) 2000-2009 Fabrice Bellard, et al.
  configuration: --extra-version=4:0.5.1-1ubuntu1 --prefix=/usr --enable-avfilter --enable-avfilter-lavf --enable-vdpau --enable-bzlib --enable-libgsm --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libvorbis --enable-pthreads --enable-zlib --disable-stripping --disable-vhook --enable-runtime-cpudetect --enable-gpl --enable-postproc --enable-swscale --enable-x11grab --enable-libdc1394 --enable-shared --disable-static
  libavutil     49.15. 0 / 49.15. 0
  libavcodec    52.20. 1 / 52.20. 1
  libavformat   52.31. 0 / 52.31. 0
  libavdevice   52. 1. 0 / 52. 1. 0
  libavfilter    0. 4. 0 /  0. 4. 0
  libswscale     0. 7. 1 /  0. 7. 1
  libpostproc   51. 2. 0 / 51. 2. 0
  built on Mar  4 2010 12:41:55, gcc: 4.4.3
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/home/nicola/Video/Miei/Telefono/VIDEO0003.3gp':
  Duration: 00:02:52.47, start: 0.000000, bitrate: 7968 kb/s
    Stream #0.0(eng): Video: mpeg4, yuv420p, 1280x720 [PAR 1:1 DAR 16:9], 60 tbr, 1k tbn, 60 tbc
    Stream #0.1(eng): Audio: samr / 0x726D6173, 8000 Hz, mono, s16
At least one output file must be specified
nicola@nicola-laptop:~$ 
###############################################

4) In this moment I haven't a short video to upload for you, but I can confirm you that all my phone 3gp videos behave the same way: video ok, audio ko.