IDG reports that Microsoft is working on the follow up to Windows Mobile 5.0, and it's code-named Crossbow. It confirmed this information with Microsoft's senior VP for mobile devices and telecoms sector Pieter Knook.

Knook said Crossbow would have robust ties to the upcoming Office 2007 suite, including a mobile edition of Office Communicator - with instant messaging and other communications applications - and Exchange 12. "As the Office [2007] PC versions of those applications improve, we're tracking that on the Windows Mobile side," Knook explained.

Microsoft released Windows Mobile 5.0 in May of 2005. Since then, an explosion of manufacturers and ODMs have picked up the platform and built both Windows Smartphones and Pocket PC Phones. It has gotten to the point where, for example, research firm The Diffusion Group predicts Redmond's share of the smartphone market will grow considerably over the next few years; overtaking leader Symbian.

In February, The Diffusion Group said that at the end of last year the U.K.-based company enjoyed a market share of 51 percent, followed by Linux (23 percent) and Microsoft's mobile platforms (17 percent). By the end of 2010, however, it predicts Symbian will fall behind both Microsoft and Linux; declining to approximately 22 percent, with Windows at 29 percent and Linux holding 26 percent.

It isn't just Symbian, Crossbow will target, of course.

As you can tell from the description above, Crossbow will continue Microsoft's assault on Research In Motion's middleware (BlackBerry Enterprise server) and handhelds begun by Exchange Server 2003 with Service Pack 2 released last fall, and continued by on-device software clients rolling out this year - introduced at 3GSM in Barcelona a few couple months back - by operators; (Palm and Verizon just released an update to bring push e-mail support the Treo 700w last week.)

"You're getting to the point right now where this quarter is really where the whole offer comes together," Knook told IDG.

For the most part, administrators stayed loyal to BlackBerry during its nearly five-year long struggle with patent holding company NTP that cost it $612.5 million dollars. Some tried out other push e-mail solutions, even if they didn't make the switch, however.

Knook asserts the amount of money enterprises can save simply by having push already a part of Exchange deployments, now that it's been integrated in the e-mail server - he estimates about $1.5 million in software alone for 20,000 users - could encourage companies to bid farewell to BlackBerry.

BlackBerry is also about reliability and speed, however. It'll be interesting to hear what enterprises and end-users have to say about Microsoft-based push solutions, after they've moved over from a RIM deployment.

Knook said it is too early to say when Crossbow may arrive. There are rumors that Crossbow will be supplied to phone manufacturers later this year, with a full-blown mobile OS redesign, codenamed Photon, to follow a year later.

Photon will supposedly finally unify the Smartphone and Pocket PC platforms of Windows Mobile under the single umbrella that 5.0 was supposed to do but didn't. Its interface may be customizable as well.

Microsoft would like to keep the mobile OS updates coming on a yearly basis from then on.