There's an increasing amount of data that suggests Windows Phone, despite Microsoft's massive marketing campaign and partnerships with any number of companies, is struggling to survive.

Microsoft always knew it'd be a hard road ahead for the platform. But as I mentioned in an eWEEK article yesterday, executives in Redmond probably harbored the hope that Windows Phone would enjoy steady and incremental gains over several quarters.

Yet that doesn't seem to be the case. Research firm comScore is estimating Microsoft's smartphone market share declined from 7.5 percent to 5.8 percent for the three-month period ending in June. That included both Windows Phone and the company's more antiquated Windows Mobile platform, which is being phased out.

Meanwhile, the Seattle Post-Intelligencer estimated Microsoft's possible revenue from Windows Phone at less than $613 million. That figure came from subtracting Xbox 360-related revenue--some $8.103 billion--from that of its overall Entertainment and Devices Division, leaving $613 million split between Windows Phone and a variety of much smaller projects such as Zune and Surface.

Even CEO Steve Ballmer's acknowledging the adoption issues: During a July 11 keynote speech at the company's Worldwide Partner Conference, CEO Steve Ballmer described the newish platform's market share as "very small."

Microsoft is betting a lot on its upcoming "Mango" update, due to final release sometime this fall. Samsung, HTC, LG Electronics and Nokia have all committed to building new Windows Phone devices preloaded with Mango, along with Acer and ZTE. Some 500 new elements to the update include expanded functionality for the Xbox Live and Office hubs, new multitasking abilities, and Bing deeply baked into the user interface.

But will Mango really reverse Windows Phone's fortunes? I find that questionable, particularly since Mango will release just as Apple's iPhone 5 (presumably) hits the market, along with a new generation of ever-more-advanced Android smartphones.

Microsoft is also pinning its hopes on a partnership with Nokia that will see the Finnish phone maker adopt Windows Phone as its mobile software platform. Following the announcement of that partnership earlier this year, a few analysts suggested that Nokia's global presence would boost Windows Phone to new market heights within the next few years. Research firm IDC, for example, even went so far as to predict that Windows Phone would overcome both Apple's iOS and Research In Motion's BlackBerry franchise to become the second-ranked smartphone platform after Google Android.

According to its latest financials, though, Nokia's bleeding market share, thanks in part to competitive pressures from the likes of cheap Android devices, and also because nobody's willing to buy Symbian OS devices that'll be effectively mothballed in a couple of quarters. If Microsoft ever harbored the hope that it'd inherit Nokia's market share for Windows Phone with relatively little attrition, that's looking highly unlikely. Nor does the partnership help solve Microsoft's issues in the United States, where Nokia has a negligible smartphone-market presence.

As I mentioned yesterday, that leaves Microsoft betting that the Mango update, combined with a massive ad campaign and new manufacturing partners, will help change its trend-line among U.S. users. Now don't get me wrong: I like Windows Phone, and I think robust competition always improves a market. But the current data suggests Microsoft's smartphone dreams are in very serious trouble.

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