Chicago is jumping onto the Wi-Fi bandwagon, announcing a plan to court private companies to build a citywide network and offer free or low-cost service.

The city already has free Wi-Fi hotspots in key downtown locations, including Daley Plaza, Millennium Park and public libraries throughout the Chicago, but now it wants to make Internet access available across its 235 square miles.

Chicago has issued an RFP and will consider proposals, leaving it to the private sector to determine the best way to build out the network and how to make it profitable, said 39th Ward Alderman Margaret Laurino, chairman of the council's Economic, Capital and Technology Development Committee. The wireless network is expected to cost about $18 million and take up to 18 months to build. Laurino said the city hopes to pick a vendor and get started within four months.

Among the companies she thinks will respond to the RFP are EarthLink, Google and AT&T, Laurino said in a Wednesday morning radio interview.

Mayor Richard Daley said at the press conference announcing the Wi-Fi plans that he also expects the private sector to step up and provide access to computers for low-income residents, as part of the Wi-Fi plan.

The city is providing access to public rights of way, such as utility poles, and could become an anchor tenant on the system as well. Chicago officials estimate the need for as many as 7500 antennas in order to cover the entire city. According to Laurino, the concentration will be on neighborhoods where residents are less likely to be able to afford Internet access.

In cities that have already built Wi-Fi networks, including Corpus Christi, Texas, and Cleveland, Ohio, the networks were initially used to provide public safety and government automation services, such as wireless computers for building inspectors to speed up service and cut down on paperwork.

Other cities that are planning Wi-Fi networks, including Philadelphia, San Francisco, Anaheim and Minneapolis, are turning more toward public-private partnerships, which allow a private company to build and operate the network, making money either by selling ads to support the service or creating service tiers that start with a low-speed free access service but charge users for higher-speed access. Selling services to the city is another means of generating revenue.