Visto has filed a lawsuit against Microsoft, accusing it of improper use of patented Visto technologies in Microsoft's software for accessing email from phones and other wireless devices.

The action kicks off another legal battle in the wireless email market. Research in Motion is currently defending a suit brought by NTP, which says RIM used NTP technology patents illegally in its BlackBerry email devices. Just yesterday, Visto said it had licensed those patents from NTP.

Visto's suit, filed in the US District Court for the Eastern District of Texas, seeks unspecified monetary damages and a permanent injunction preventing Microsoft from shipping the software in question, Windows Mobile 5.0. Visto called the product "a blatant infringement on Visto's patented technology".

It also accused the software maker of routinely stealing technologies from smaller companies and settling subsequent court cases with hefty payments.

"It's the obligation of this company to protect our ability to compete on a fair and level playing field," said Brian Bogosian, chairman, CEO and president of Visto, in a conference call following the announcement.

Bogosian claimed that Microsoft's move into providing 'push' email software, which delivers messages instantaneously to mobile devices, infringes on patented technology developed by Daniel Mendez, co-founder and current senior vice-president of intellectual property at Visto. The firm did not speak to Microsoft about a licensing deal prior to filing the lawsuit, believing it is the software giant's responsibility to determine whether it is infringing upon another company's intellectual property before it enters a particular market, Bogosian said.

Visto's patents apparently do not extend to the concept of a wireless email system patented by NTP. Bogosian said Visto obtained a licence for those patents because it recognised the validity of the patents, and out of respect for intellectual property owners.

He declined to reveal how much Visto paid for the licence, or how much of an equity stake NTP took in the company as a result of the deal, but said the total value was less than $450m. That is the same amount that RIM had agreed to pay NTP in a settlement earlier this year before that deal collapsed, setting up a possible injunction against the sale of RIM's BlackBerry devices and service in the US.

Microsoft declined to comment beyond a brief statement distributed by its public relations agency, Waggener Edstrom. "Until we have an opportunity to see and review this complaint, we're not in a position to comment on it. In the meantime, however, let us underscore that Microsoft stands behind its products and respects intellectual property rights," the statement read.

Visto's software is used by carriers including Cingular Wireless, Sprint Nextel and Vodafone. Its lawsuit accuses Microsoft of infringing on three US patents in particular. They are patent number 6,085,192, entitled 'System And Method For Securely Synchronizing Multiple Copies Of A Workspace Element In A Network'; 6,708,221, 'System And Method For Globally And Securely Accessing Unified Information In A Computer Network'; and 6,151,606, 'System And Method For Using A Workspace Data Manager To Access, Manipulate And Synchronise Network Data'.

Patents can be viewed by searching the US Patent and Trademark Office website.