We've received word that the newly shipping 16GB iPhones can indeed be jailbroken, providing read/write access that allows the installation of unofficial third-party applications. They run iPhone OS 1.1.3 out-of-the-box, which can be readied for apps via these instructions then used only on approved iPhone networks (AT&T in the US, O2 in the UK, etc.)
Jonathan Zdziarski, one of the most noted underground iPhone developers who has been instrumental in developing numerous jailbreak methods and recently released a book dubbed "iPhone Open Application Development" writes:
"I decided to go and buy a 16GB for testing. It does, in fact, jailbreak properly and run on approved networks."