RIM's BlackBerry smartphones have long dominated corporate mobile communications with on-the-hip email and security credentials, but are increasingly challenged by Apple products and smartphones running Google's Android software.

"We are making this transition in order to better support our mobile applications initiatives," spokeswoman Tara Mullee Agard said in an email on Tuesday.

The Houston-based company will switch 4,500 BlackBerry-toting employees across to iPhones over the next two years, Mullee Agard said, adding that Halliburton would supply the devices. Apple is helping with the transition, she said.

Even before a major RIM outage last October left many workers without email on their BlackBerry, companies had been considering alternatives.

Last year, Credit Suisse started allowing bankers to use their Apple and Android devices on the company network - one-third of its 25,000 BlackBerry users have switched.

Barclays Capital also allows some employees to use iPhones and iPads. Standard Chartered switched from BlackBerry to iPhones for many users last year.

Companies that had previously supplied workers with a BlackBerry and paid RIM a monthly service fee can save by encouraging use of personal devices.

Yet while many large corporation say they are testing how the iPhone and other devices can handle their email and other corporate data, it is unclear how many will ultimately abandon the BlackBerry entirely.

RIM has nevertheless recognized the threat and in November announced it would offer security features for iPhone and Android from within its existing BlackBerry service for corporations.

(Reporting by Alastair Sharp; editing by Rob Wilson)

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