PC World – Fourth-generation (4G) wireless broadband is still in its infancy, and the nation’s cellular carriers are working out the kinks of their respective 4G implementations. AT&T and Verizon Wireless plan to implement Long Term Evolution (LTE) service either late this year or early into the next. And Sprint, in conjuction with Clearwire, a small carrier it has a controlling interest in, is already using WiMax for its 4G service in a few dozen U.S. markets.