By Daniel Eran Dilger

Published: 05:25 PM EST (02:25 PM PST)

Two of America's largest banks are actively testing Apple's iPhone as a replacement of their existing RIM BlackBerry devices for corporate email.

According to a report by Bloomberg, the two banks are evaluating the security of new software designed to support corporate messaging on the iPhone.

Bank of America, the largest bank holding company in the United States, and Citigroup, the world's largest financial services network, each employ over a quarter million people.

The trials reportedly involve over a thousand users between both banks, although neither has made their plans public yet. Both banks were among the first to support Apple's iPhone App Store with custom banking apps with the ability to perform secure transactions.

Update: AppleInsider has also heard from a source who reported Citigroup "is also testing iPad for remote workers and business travelers." A second reader reports that Zurich Financial Services is "also testing the iPhone and some proprietary applications to replace BlackBerrys."

BlackBerry's slip, Apple's grab

Once seen as protected by extreme customer loyalty, RIM's BlackBerry platform is now eroding in large part because the company hasn't been able to deliver a competitive user experience or vibrant third party app ecosystem outside of the company's forte in mobile messaging.

The Bloomberg report cited research by Sanford C. Bernstein & Co, which noted that among 200 companies that officially use BlackBerrys, 83 percent allowed their employees to use other devices as well. "Cost savings and employee preference were the two biggest reasons cited by companies for the shift in the study," it stated.

Companies have responded positively to Apple's iPhone in large measure because the company has made enterprise support a key engineering priority, adding features such as Exchange Server messaging, enterprise authentication methods, VPNs, corporate management of profiles, and remote wipe.

Following the company's efforts to make iPhone attractive to corporate users, Apple executives have noted dramatic increases in interest from Fortune 500 companies, with its chief executive Steve Jobs claiming 80 percent adoption or evaluation by America's largest companies last month.

Apple has also recently contracted with Unisys to develop secure software for iOS devices in order to attract new corporate and government sales.

Limited corporate maturity in Android, WP7, HP Palm OS

Companies are also evaluating other smartphone platforms, but running into issues with weak support for security and integration. The latest version of Android still lacks functional support for Exchange (particularly hardware encryption), 802.1x WPA2 wireless network authentication, corporate proxy servers, Cisco VPNs using certificates, OpenVPN, CalDAV, remote wipe, and managed apps and configurations.

Microsoft's Windows Phone 7 and HP's Palm webOS are brand new and untested in corporate circles. Both are starting virtually from scratch, as Microsoft has ditched its pervious Windows Mobile platform to sell the entirely new, incomparable Silverlight-based WP7, while Palm released its webOS new from the ground up just months before HP's acquisition.

That hasn't stopped Dell from announcing a wholesale abandonment of its existing RIM corporate messaging infrastructure in order to move its 24,000 employees to Dell-branded devices running Android or WP7. Microsoft itself has been marketing its new WP7 devices to consumers, and maintaining an old version of Windows Mobile as its solution for enterprise users.