Updated from 1:18 p.m. EST

The wireless email patent dispute that has ensnared Research in Motion ( RIMM) is now expanding to include software titan Microsoft ( MSFT).

Redwood Shores, Calif.-based Visto, a startup that makes a platform for wireless push email that competes against RIM, announced Thursday that it has sued the world's largest software maker. Visto, established in 1996, is alleging that Microsoft's Windows Mobile 5.0 operating system for mobile devices infringes on three of its patents related to mobile access to email and data technology.

Visto, which holds 25 patents and has 57 patents pending, is seeking a permanent injunction against Microsoft and monetary damages. Visto's suit against Microsoft comes one day after the company announced it had received an equity stake from NTP, the Virginia-based patent holding company whose suit against RIM threatens to shut down its popular BlackBerry service in the U.S.

Visto's deal with NTP also includes an agreement to license NTP's patents.

In a telephone press conference Thursday, Visto Chairman, CEO and President Brian Bogosian said the company did not attempt to negotiate with Microsoft before filing the suit and argued that the Redmond, Wash., company was well aware of Visto's products and that Visto even had been named a preferred solution for mobile operators using Microsoft's operating system in February 2004.

"We looked at this very closely...we felt it was very black and white," he said. "We had very little expectation...that Microsoft would take any of our claims very seriously."

Visto said Thursday that its concerns were heightened by Microsoft's recent bundling of Windows Mobile 5.0 with its Exchange server software. "This method of bundling software has led Microsoft to be prosecuted by competition authorities in the past, and in this case, potentially increases the rate and manner in which their infringement on Visto's patents occurs," Visto said in a press release.

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