(keitai-l) [N503i] How to completely clear the memory?

Sorry if this question has been answered before; I couldn't find it on a 
web search.

I'm about to leave Japan, and I wanted to make sure my keitai's memory 
is completely clean before I return it.  How can I do a full reset on my 
N503i?

I have the English manual (2001-02 edition) for my DoCoMo N503i phone, 
and it does have a "Function Reset" to return the configuration to the 
original settings, but that leaves all the iAppli, phone numbers, call 
records, chakumelos, and other data in place.

I tried leaving the battery out for a while, but I think all this data 
is stored in flash ROM. I read the manual from cover to cover (I'm a 
pretty technical guy) but I couldn't find the answer anywhere.  I also 
tried a few Japanese web searches, even asked my Japanese co-workers, 
but nobody could find an answer.

Thanks to anyone if you know the answer.

Ben