answer:I have used two devices running on windows mobile 5, one treo, one sidekick running the danger OS and have played with the blackberry a bunch. The sad answer is none of them. But it terms of which is closest, I’d say the sidekick. Wonderful keyboard, very nice user experience (was by far the best before the iphone showed up), incredible OTA sync that leaves every other phone in the dust, plays songs, etc. After that, I’d say the blackberry, although it is focused on different uses than the iphone. After that, nothing. PalmOS is in bad shape, and Windows Mobile makes Windows Vista look intuitive and Windows Me look stable. Avoid at all costs.