HELSINKI (Reuters) - Nokia smartphones will be able to access IBM Lotus Notes corporate email starting from next month, the two firms said on Thursday, as the world's top handset maker battles Blackberry-maker RIM.

Nokia said thanks to the new software more than 80 million users of its smartphones can access IBM's Lotus email. In September Nokia signed a similar deal with Microsoft, the leading corporate email provider.

"With this partnership we are able to mobilize close to 90 percent of corporate emails without any extra investments from corporations," Ilari Nurmi, VP at Nokia, told Reuters.

"A lot of companies have servers in place and a lot of Nokia devices on the premises. It's an important factor in cost-conscious times," Nurmi said.

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Nokia dropped development of its own corporate email product this year, choosing to look for partners instead while focusing on developing phones for business users to better challenge RIM, the leading mobile email vendor.

"Since revising its business strategy, Nokia has sharpened its focus and is turning up the heat on RIM and Microsoft, particularly in the SMB segment," said Geoff Blaber, analyst with research firm CCS Insight.

"Adding support for Lotus Notes is a huge step forwards. The move gives Nokia the capability to target a much broader market and a segment where RIM has dominated to date."

The announcement comes against a backdrop of falling demand for cellphones worldwide as the global economy falters, with Nokia warning last week that it expects industry volumes in 2009 to contract.

Some analysts have tapped smartphones as the market segment with the best hope for growth in 2009.

In the third quarter Nokia sold 1.1 million of its new sleek, full-keyboard E71 phones, outselling RIM's business user-targeted Blackberry Bold by five-to-one, according to Nokia.

However, Blackberry Bold went on sale in its key United States market only in the fourth quarter.

Last week Nokia unveiled a somewhat stripped-down version of E71, the Nokia E63, which is expected to begin shipping in the coming weeks for an estimated retail price of 199 euros before taxes and subsidies -- almost half the E71s estimated retail price unveiled in June.

Nokia's Nurmi said the E63 could well outsell E71.

"From affordability standpoint there is clearly bigger potential for this product," he told Reuters.

RIM's dominant position in the mobile email market was not set in stone.

"This is not a mature market. We are all going to grow the market," said Kevin Cavanaugh, vice president of IBM Lotus Software. (Reporting by Tarmo Virki; Editing by Jon Loades-Carter)