Engadget posted an in-depth preview of Windows Phone 7.5 Mango

Make no mistake, Microsoft isn't playing coy in the smartphone market any longer. The folks in Redmond are making a significant jump forward in the mobile arena, announcing that the upcoming version of Windows Phone, codenamed "Mango," will be heading to a device near you in time for the holidays. As its competitors have raised the bar of expectations to a much higher level, Microsoft followed suit by adding at least 500 features to its mobile investment, which the company hopes will plug all of the gaping holes the first two versions left open.

We received a Samsung Focus preloaded with the most recent developer build (read: not even close to the market release version) and we had a few good days to put it through its paces. It's still far from completion, as there were several key features that we couldn't test out; some weren't fully implemented, and others involved third-party apps that won't be updated until closer to launch. Yet we don't want to call this build half-baked -- in fact, it was surprisingly smooth for software that still has at least four months to go before it's available for public consumption.

  Windows Phone 7.5 Mango in-depth preview