You have the MPx220, so that's a Smartphone. No touch screen, smaller foot-print, focused on being a phone first and a data device second. Smartphones are a one-handed device, in that you can do everything with one hand.
The JAM, KJAM, PDA2K, Treo 700w, etc... are all PPC-PE devices. Typically they are a little bigger and more power hungry. They have a touch screen, and are meant as a "connected" data device. So they are better suited for data duties first, and act as a phone second. The PPC-PE devices are not that good at being one-handed. You'll find that you have to use the stylus or your thumb to tap things out on the screen at times.
The line is getting blurry, and the next major release of Windows Mobile - code named Photon will merge the two platforms. So there will no longer be a difference. There will only be Windows Mobile.
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