Wireless can be used to cover a whole city. Usually this is ISP's that have something set up. You also need to see what the laws are for your country are not all countries allow it. There are Base Stations and NON-Line of site Antennas but they are from other companies and not from cisco.
But remember that if we are talking of 802.11* standards then we are talking of using unlicensed radio frequencies, as opposed to GSM. So technically speaking, you can cover whole city with your wireless network but you cannot guarantee your customer this will work everywhere undisturbed. Opposed to GSM of course.
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