NEW YORK — Sprint Nextel Corp. said Monday that it has turned on its new wireless data network, providing a much-needed boost to the carrier, whose data speeds lag those of its largest competitors.

Sprint fired up the fourth-generation, or 4G, network in Atlanta, Dallas, Houston, Kansas City, San Antonio, and some smaller surrounding cities on Sunday. It uses LTE, or Long-Term Evolution, technology already in use by Verizon Wireless and AT&T Inc.

PC Magazine got early access­ to the network a month ago and found that it’s not quite as fast as Verizon’s and AT&T’s equivalents, but a big step up from Sprint’s older 3G, or third-generation, network and the 4G access it rents from Clearwire Corp.

Sprint, the third-largest US cellphone carrier, doesn’t have as much available spectrum, or space on the airwaves, as the larger carriers do. That holds back its LTE speeds somewhat.