I've had better luck with using PCM audio, it takes more file space, but puts less strain on the blackberry. I've actually found the best bitrate for mpeg4 videos is about 512, but ~320 will do fine.

I've actually been using virtual dub to image crop and scale, and time scale over mencoder, as mencoder has issues with adding an offset to the audio. I haven't seen a way to disable this.

Virtual dub can be downloaded at:
Welcome to virtualdub.org! - virtualdub.org