Originally Posted by blinki bill

You are giving two presets "baseline" and "slower" which won't take, one will be ignored, so for max compatibility with mobiles you should probably just use "baseline".
Note that "-vpre" is deprecated, you should use "-preset" to set it instead, also if you don't set "-preset" at all, or use "-vpre" the "-crf" won't take.

I would suggest making some tests like this:
ffmpeg -i $src -vcodec libx264 -s 320x240 -preset baseline -crf 25 -acodec libfaac -ac 2 -ar 44100 -ab 64k $dest_mobile

Me personally - For resolution I allow up to 480p so if the source has lower res I just pass it as it is and if it's higher I scale it down to 480p, for quality I use "-preset slow" and "-crf 23". I don't like to lower the resolution for older mobiles, it really punishes modern devices with displays that will make a laptop look like a "caveman", 480p as a max seems like a good mid point for me. In my testing iphone 4+ works fine with my files, I also tested on 2 old android phones with android 2.1 and 2.3 (one was as bad as single core 600mhz procesor no gpu at all) and it worked there too, so It's fine enough for me