Widespread wi-fi
Under the series of deals that BT has signed with local councils, tin can-sized antenna will be fixed to street lights, bus stops, phone boxes and park benches to make the wireless net access available across broad swathes of the 12 cities.
BT said deals had been signed with Birmingham, Edinburgh, Leeds, Liverpool, Cardiff and Westminster in central London and added that announcements about six others were "imminent".
The wi-fi zone technology has been trialled in Cardiff and Westminster and the networks set up in these areas will now be extended.
"This first phase of 12 cities is just the start," said Steve Andrews, BT's head of converged communications services in a statement. "We are already negotiating with many other cities."
Mr Andrews said BT was spending millions on the schemes.
People were likely to use the wi-fi for net access but BT said that the network of antenna could be put to other uses. For instance, it said, they could be used to support more widespread CCTV systems or to give real time information about traffic jams or parking spots.
BT said that the first users of the wi-fi zones were likely to be workers toting laptops but also expects rapid growth in the numbers of smartphones that use wi-fi to make and take calls.
BT aims to split the cost of setting up the schemes with councils and share profits from information services that use the wi-fi networks.
In an unrelated initiative, wi-fi network firm The Cloud is also setting up wireless zones in nine cities including London, Manchester and Birmingham.