Flash would be great. Currently the 8xxx Series packs a 312mhz CPU. There are times Flash Support ties up the CPU on my Desk so I assume it would wipe out the Blackberry. I am stoked our devices support JavaScript. RIM prides themsevles on security and apparently they found a level comfort in JavaScript and made it even better in the 4.7 release. I would assume Flash adds to many unknowns for implementation at the time and I would also guess Apple would add it first.
Actually there are quite a few devices/phones that support a flash player, albeit a scaled down version that Adobe calls FlashLite. Most Nokia devices offer support as well as many non-business focused devices. In the upcoming year you will probably see a new version of the mobile flash player that will make use of the Flex framework and utilize AS3. When that happens then there will be some ultra powerful web/flash apps for mobile. Right now it's available but not as robust as the typical flash player found on a laptop/desktop.
iPhone will probably hold off until Adobe develops a version of the Flash Player that Jobs feels is appropriate for the device. He has complained that the Flash runtime is to heavy for Mac OS X and that flashlite is not powerful enough for the iPhone.
Ajax support on the bb would be a nice first step, although I would be all over a flash capable browser.