Just how big can mobile E-mail get? The BlackBerry may seem ubiquitous in certain circles, but there are only somewhere around 5 million mobile E-mail users of all stripes today. Imagine 20 times that many.

"We think that 100 million users in four years, just in the enterprise market, is very achievable," said Dave Grannan, general manager of mobile E-mail at Nokia's Mobility Solutions division, speaking at Interop, a conference on technology convergence, in New York on Tuesday. Grannan said a variety of factors will drive that growth, including new mobile devices that will come standard with E-mail, such as devices coming from Nokia starting next year.

Hovering over the discussion was the future of the BlackBerry service, since maker Research In Motion Ltd. faces a patent lawsuit by NTP Inc. that threatens to shut down the service in the United States. RIM has declined to discuss a report by The Wall Street Journal and others that NTP Inc. would settle its patent-infringement lawsuit against RIM for a payment equal to 5.7% of future revenue from BlackBerrys sold in the United States. But Dave Werezak, VP of RIM's enterprise business unit, said shutting down the BlackBerry service in the United States wouldn't benefit NTP. "There's no advantage for anyone to turn the service off," Werezak said.

If that 100 million figure is reality, and BlackBerry can keep running, it's well positioned for growth. BlackBerry is one of the most popular devices for mobile E-mail, and about 60% of businesses running the BlackBerry Enterprise Server have started deploying other applications beyond E-mail, the company says. Shutting down RIM's BlackBerry service means hurting customers that are using or deploying BlackBerrys and RIM's mobile E-mail service, which is the driving force behind wireless deployments at many companies.

Other panelists voiced the importance of the BlackBerry for business users. "RIM has done a great job in proving that there's real value in mobile E-mail," said Jeff Damir, VP of sales and business development at Seven Networks Inc., a provider of mobile E-mail software.

The key to major growth of mobile E-mail is whether businesses start deploying devices like BlackBerrys to the rest of the workforce, beyond executives and road warriors. Said RIM's Werezak, "We see potential for people you wouldn't automatically think of getting these devices, like jobs in facilities and the IT staff that needs [the devices] to work through trouble tickets."