have a look at tcpmp forums http://tcpmp.corecodec.org/, there are encoding guides for palm and other low performance PDAs so they take it also from the performance point of view (i.e. what is costly to decode)

one pointer
http://www.corecodec.com/index.php?o...0&topic=1332.0

As for the guide mentioned above, it looks good. I don't think the information about N770 audio is true (32Khz maximum) but otherwise it is definitely useful.