The announcement represents a shift to multisource service relationships, and both deals result from competitive reviews and "significantly change" the structure of such relationships, according to the bank.

CBA CIO Michael Harte said the new arrangements will deliver more efficient operations and significant service improvements, and reduce costs across the enterprise.

"Moving to a new supplier for the mobile service will provide a higher level of service for end users within the bank, increased flexibility and associated accountability, with reduced overall costs," Harte said.

The extension of its IT outsourcing agreement with EDS Australia is specifically for the provision of mainframe and mid-range data processing services (collectively known as Enterprise Processing Services) for a period of six years to June 2012.

While the $573 million deal is significant, it is a far cry from the 10-year, $5 billion outsourcing partnership inked in 1997. Projects since 1997 include a refresh of 40,000 desktops, rationalizing 38 disparate office environments to two, upgrades to the ATM network, the CommSee customer management system, an Internet banking infrastructure replacement, and applications work for the bank's lending systems.