When I bought a Torx T6 screw driver to replace MacBook Pro’s hard drive, I realized that the same screwdriver can be used to open P990i casing. So, I opened the casing, and I can pull out the old stylus. The stylus was stuck in a spring mechanism which I guess used to prevent the stylus from falling to easily.
You can look the disassembly pictures at
my photo album.
One thing that may not be clear from the instructions on the Internet is this: To open the part that covers the front camera: pull it upward (that is toward the upper side of the phone).