Motorola management’s efforts to keep upstart billionaire investor Carl Icahn off the board were rebuffed by a shareholder advisory service today, increasing the pressure on Motorola to open up to Icahn’s proposal to overhaul the company’s business model. Meanwhile Motorola announced that its venture arm infused an undisclosed amount into enterprise wireless company Vocera Communications Systems.

Institutional Shareholder Services today recommended that Moto shareholders elect Icahn to the board, from which Icahn plans to pressure the company into increasing its profit margins and return more cash to its investors. But another shareholder advisory group, Glass Lewis, today came out in favor of Motorola’s current board and management. Icahn, who owns 2.9% of the company’s stock is up for election at Moto’s annual board meeting on May 7.

“It’s more likely than not that Icahn will act as a positive influence on the board by providing a fresh perspective,” ISS said in its report released today.

Opposing Icahn’s nomination is CEO Ed Zander, who has been struggling to turn around Motorola’s fortunes after two years of rapid growth in the handset market ended last year. Motorola’s global market share for handsets dropped to 17.5% in the first quarter after increasing to more than 22% in 2006, and it reported its first sales drop in four years. Zander, however, has claimed that Icahn lacks experience in the technology sector and refused to endorse his nomination, leading Icahn to start a proxy fight.

Motorola Ventures, its strategic venture capital arm, today said it made an equity investment in Vocera, which makes a badge communication technology for hospitals and other vertical markets. Vocera uses voice recognition technology and Wi-Fi to communicate spoken information across a hospital’s network, allowing doctors and other health care workers to communicate instantly with colleagues or retrieve critical information from the network. Financial terms of the deal were not disclosed.