Two will be in Belfast and one in Portadown, County Armagh.
BT Managing Director Alastair Hamilton said the new network would have important benefits for businesses and help to attract more inward investors who demand high speed communications.
However, he added that domestic customers would also see an improvement in service - the system will triple the speed of broadband internet access.
Work has already started across the UK on the project, but Northern Ireland will be the first to complete its new network in 2010.
