It's hard to keep up with the patent suits flying among mobile phone companies.

On Friday, Microsoft joined the ring, with a suit leveled at Motorola's Android-based smart phones, filed in the International Trade Commission and the federal court in the Western District of Washington. The suit charges Motorola with infringing on its patents related to "synchronizing email, calendars and contacts, scheduling meetings, and notifying applications of changes in signal strength and battery power." (See the statement from Microsoft's in-house IP lawyer Horacio Gutierrez below.)

Motorola disputes the charges.

The move comes as Microsoft is preparing to launch its Windows Phone 7 operating system, an upgrade to its disappointing Windows Mobile franchise. On Friday the company announced a new mobile chief, Andy Lees, to take charge of its product efforts and try to claw back some relevance there. Its most recent effort, the Kin, was killed almost as soon as it launched.

Next up: Windows Phone 7, with smartphones based on the OS reportedly in the wings from South Korea's Samsung and LG Electronics and Taiwan's HTC, which are expected to be announced next month.

Early reviews of Windows Phone 7 have been mostly positive, drawing comparisons to Microsoft's popular well-received (thanks SaintWaldo!) Zune and XBox products, rather than missteps like Vista. Microsoft invited Wired.com's Gadget Lab reporter Brian Chen to Redmond for a demo this week, he seems favorably impressed. Check for his report next week.

The legal shot at Motorola and Android is just the latest scuffle in the crowded smart phone market, which has seen similar suits fly between Blackberry maker RIM and Motorola (settled); Apple and Nokia; HTC and Apple; and Oracle and Google (over Java).

Market research firm Gartner predicts Nokia's open source Symbian OS will hold a 40.1 percent of the mobile operating system market share at the end of 2010 followed by Google's Android with 17.7 percent, RIM's BlackBerry with 17.5 percent, Apple's iOS with 15.4 percent and Windows Mobile from Microsoft with 4.7 percent.