It's my understanding that Apple will issue a number of capacity sizes naturally, however, for another $5000, the iboob capacity can be enhanced to the next biggest size.
Interestingly, there have been reports of some owners paying to reduce the iBoob capacity...
Howbout you just keep it in your pocket if you feel like you are in an area where it could be stolen? Other wise, people are not going to be jumping at you wherever you walk to try to get their mits on your phone. Its just a phone.