"JackFlash is an application that loads some of your memory hogs into Flash ROM, thereby freeing up some precious memory space on your Palm. To use JackFlash you have to have Flash memory. Palm IIIes and Visors don't have Flash memory, so you're stuck with 2 MB if that's what you've got. Palm VIIs use all of the Flash ROM space so JackFlash won't work on them either."

http://www.geek.com/hwswrev/palmpilot/jackflash.htm