Didn’t know this. Apparently you can turn an old ball point pen into a stylus. LSN Global has created the ECOPLUS ballpoint pen cartridge which comes with a nib similar to what we see for the current crop of styli. Of course this only works on passive screens.
That said, you might want to listen to some interesting info from Hugo Ortega on this GBM podcast. According to Hugo there is a defintie relationship between an OEM’s stylus and the screen and he recommends staying true to the stylus and replacment nibs offered by the manufacturer of your device.