HOW-TO: modify profile files

[Stefano Galizia - Yahoo]

Hi to all,
I've following need:

        Change a profile file programmatically.

When a user hang-up a call i've to change the ringtone used in the profile.
My problem is that i don't know how to change the,e.g. profile0.dat, file. I
think the last two bytes of this file are checksum but i don't know how to
calculate it.

Anyone can help me???

Thanks