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(Reuters) – Shares in Research In Motion slipped more than 3 percent on Friday morning as investors fretted the BlackBerry smartphone’s stranglehold on corporate communications was being eroded by rival devices.

Bank of America and Citigroup have joined a growing throng of financial institutions eyeing alternatives to the BlackBerry for corporate email.

The banks are testing software designed to make Apple’s iPhone secure enough for company messages, Bloomberg said, citing three people familiar with the plan.

A source at Bank of America confirmed the details of the report. A Citi spokeswoman declined to comment.

BlackBerry smartphones have long been the device of choice for bankers, politicians and executives who need secure access to email and the Internet when outside the office.

But the surging popularity of consumer-oriented smartphones such as the iPhone and devices running on Google’s Android software, coupled with their makers’ moves to boost security credentials, are pressuring RIM’s dominance in the corporate sector.

Allowing the rank and file to access corporate email on personal devices also saves companies the cost of supplying a BlackBerry.

"If the IT department’s security concerns can be addressed it seems to be a win-win" for employers and employees, said James Cordwell, a London-based analyst at Atlantic Equities.

In a September survey, Bernstein Research found 83 percent of U.S. businesses allow employees to use non-BlackBerry alternatives to access corporate email.

On Thursday, PC maker Dell said it was moving 25,000 BlackBerry-wielding employees over to its own line of smartphones as it eyes gains in the mobile device market.

Dell said the move will save money, but RIM disputed that, noting the cost of buying, deploying and supporting new devices.

"We find it highly unlikely that they will actually save any money with this move and far more likely they were looking for a little free publicity," Mark Guibert, RIM’s senior vice-president of corporate marketing, said in an emailed statement.

"Plus, consider the fact that BlackBerry smartphones are far more efficient with respect to data usage, which means that their monthly service charges will also likely increase," he said.