Pazera Free Video to 3GP Converter
Full user review
"Does just what is says, perfectly"
Allows you to tweak video and audio settings for even the weakest phone. Mine is a 2+ year old, crappy Nokia flip phone.
Compresses vids very nicely.
Presets for certain models of phones would make things easier when tweaking video settings.
It's a damn simple cut and dry program. The presets are adequate, and can be easily tweaked and saved to get the maximum quality your phone can handle.