>> Other "facts" that it mentions are:
>>
>
> <snip>
>
>> - *3370# will activate a "reserve" battery power for emergencies when
>> your mobile is very low on power - always assuming that there's
>> enough power left to turn the phone on at all!
>>
>
> Think there might be *SOME* truth in this one. I read somewhere that this
> switches the phone into a slightly lower quality codec which could have a
> tiny effect on the power consumed...(??) (or maybe I dreamed it...) :-)

You're not far off...

*3370# turns Enhanced Full Rate (EFR) on and #3370# turns it off (back to
FR).
*4720# turns Half Rate on and #4720# turns it off (back to FR).

http://home.planet.nl/~rickvdw/nokia..._codes_en.html

Benedict.