BT will manage LogicaCMG's voice, data, local area network and mobile network infrastructure.
With the roll-out beginning in the UK, the seven-year deal will be extended to cover additional key LogicaCMG geographies in the coming months and years.
As part of the agreement, LogicaCMG and its customers will be able to benefit from BT's £10bn 21CN IP network, which is being rolled out between now and 2011.
Jim McKenna, chief operating officer at LogicaCMG, said, "BT is an expert in network management and is also active in 170 countries.
"These factors will ensure that as LogicaCMG and its customers grow, our partnership with BT will provide the expertise and network coverage to meet all of our needs."