Surprisingly, iPhone software/firmware update 1.1.4 can still be jailbroken -- for the use of unofficial third-party applications -- via some currently available methods, including ZiPhone (for full instructions, see this page). Previous software/firmware updates from Apple have broken jailbreak methods. (the tool "iJailbreak" does not work with 1.1.4)
After jailbreaking, the iPhone should be restarted once in order to restore normal phone functionality for devices used on authorized networks.
UPDATE: iPhones running software 1.1.4 used on unauthorized networks cannot be artificially activated with current tools. The developers of the jailbreak methods will need to do some additional work to get this process working again.