Test Windows Phone 7 on iOs or Android
aka.ms
aka.ms
By comparison, Android (and I came from a Nexus One before this, so I know it well) is such an un-unified mess. I find myself fighting the UI often. Windows Phone has what I genuinely think is the best mobile UI out there, bar none.
Once they improve the Maps app (it's awful), add more third party hooks (so I can get GChat etc. in the Messaging section) and people start supporting the browser more (the IE in Mango is fine, but people seem to use too many -webkit- prefixes) I'll happily switch back. In the mean time I'll be developing WP apps in an emulator...
But a compelling slideshow at that.
The freedoms that we take granted on PCs(running Windows 7 on Macs) seem to be lost now.
I think there's little stopping you from hacking around and getting each mobile OS to run on the other's hardware, but the effort to utility ratio is so low since your hardware will be severely outdated by the time you're done.