Mobile movies. MP4 or Real Media?

Recently I am learning about video formats
for mobile devices like Smartphone or PDA.
After trying compressing and converting some
of my video and music files. I learn these thing:

• AMR-NB codecs is bad. You certainly not going to get
  enjoyable experience listening to sound in this codecs.
  Unless it is purely speech.
• MPEG4 video with AAC audio is very good but it has big size and
  only playable in newer model of mobile devices
• Real Media is good however it is very proprietary.

So what video format should I choose? Any good advice?