Under the £12.5m, five-year deal, BT will build and manage a Metropolitan Area Network (MAN), to replace the police's existing analogue network.
Colin Carey, Assistant IT Director of GMP, said: "This new network will ensure that GMP utilises the latest technology to help us to reduce crime and disorder.
The MAN, which will increase data access speeds by up to 200 times, is based on Nortel Networks technology. It will integrate the police force's existing voice systems into a single broadband platform and allow for migration to full voice-over Internet Protocol (VoIP).
John Conlon, client director for BT central government, justice and police, said: "The police have many mission critical systems and it was important to offer an evolutionary approach that protected existing investment and did not disrupt existing operation. This solution," he added, "will provide a benchmark for other police forces."
An optical fibre network will link 120 sites and network management tools will allow the Force the flexibility to boost bandwidth where it is required.
"In the past, " said Conlon, "if the police wanted to set up an incident room they were often constrained by infrastructure. Now they will be able to deliver services where required without having to reconfigure the network,"
The system, which will become operational in June, will ensure that Greater Manchester Police has the necessary bandwidth to successfully deploy standardised IT solutions being promoted by Pito, the Police Information Technology Organisation. Some forces have found that their network limitations undermined the usefulness of Pito backed systems.