I have to agree with deltavolt, the new iPhone looks like it will be a very good purchase.
Windows mobile is a OS that I have always hated after having to use it for a few months. It was slow, clunky and rather useless. The new WM 7 looks considerably better as it gets rid of almost everything WM 6.5 was. However, it is still a very new platform and as such it is missing quite a few features. I am sure these features will come in future updates, but currently I wouldn't go for it.
Blackberry is a very good commercial phone, although the iPhone is very rapidly catching up. In its current form, Blackberry is a little dated and requires some newer handsets and a better OS.
You could also look at some of the Android phones, they are very good competitors to the iPhone. If you want flash on your phone - although I have no idea why you would - then Android is what you'll want.
Overall, I think waiting for the new iPhone is the best choice you could make.