codec - nokia key code to tell what codec?

Hello;

Is there a "secret" code to tell what the audio codec is in the phone? Or is it a function of the flashed program and if so is there a listing telling what codecs are in what phones? I have 3510i, 3560 (tdma), 3585i, & 3595 phones and they all sound very different. I am guessing that the 3510i uses the 06.10 GSM defined codec? Can it change codecs on command from the network?

Thx.... this all started when those "secret" enhanced full rate, half rate, etc codes no longer worked on any of the new phones (are there new codes or did they do away with enhanced full rate, half rate, etc?