Performance is good when you're sitting in an office or cafe, but don't count on connecting from a moving train or car.

Just a couple short years ago, many people were abuzz over metro Wi-Fi experiments in Philadelphia, Houston, and San Francisco, only to see those efforts largely collapse as slow speeds, expensive deployments, and economic tussles between carriers and municipalities resulted in low adoption. But waiting in the wings for several years has been the promise of WiMax technology to deliver broadband connectivity wirelessly across entire cities with less equipment to deploy than metro Wi-Fi. After nearly two years of uncertainty, Sprint and its partner Clearwire are now starting to set up WiMax networks in several cities.