I don't have a lot of experience with the 3GP container, but I wanted to have a stub page to point to what little I do have.

You can see the Samsung Gravity 2 page where I encoded video successfully for that device.

Most importantly, the specs I used:

  • AMR audio codec
  • 1 audio channel
  • 8000 hz audio
  • 12k audio bitrate
  • MPEG-4 simple video (H.263)

There's probably more support for it, but this is limited to my phone. It's a bit of a pain putting stuff on there, so I'm gonna pass on more testing.