Sprint Nextel Corp., the nation’s third-largest cellular provider, says it will use an emerging technology called WiMax (a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL) to build a new high-speed wireless network. The company said the new network, expected to be available in the fourth quarter of 2007, will provide consumers with wireless Internet speeds on par with DSL and cable TV modems. Gary Forsee, Sprint’s chief executive, said the telecom company will spend $1 billion on the network in 2007 and between $1 billion and $2 billion in 2008. The initiative was announced less than a week after the company, formed last summer by the merger of Sprint and Nextel Communications, reported a 38 percent drop in second-quarter profit. The report, which depicted a company struggling to attract and retain higher-paying subscribers, sent Sprint nextel’s shares to a 52-week low. Though derived from the same technology as the popular Wi-Fi standard that provides wireless Internet access in such places as airports and coffee shops, a WiMax signal can cover whole cities or regions.