The merger of Sprint Corp. and Nextel Communications Inc. closed yesterday, creating a company with more than 44 million mobile phone subscribers. The new Sprint Nextel Corp., with headquarters in Reston and about 80,000 employees nationwide, is betting on the explosion in wireless communications and will shed its slower-growing local telephone business.

Sprint Nextel stock will start trading on the New York Stock Exchange on Monday under the ticker symbol "S" once used by Sears, Roebuck and Co.

Despite the completion of the roughly $35 billion merger, nothing will change immediately for Sprint and Nextel mobile phone customers. Both will continue to use their old telephones under their existing service plans for the next few weeks. At some point in September, customers will be able to switch from one provider to the other without paying cancellation or activation fees.

Sprint spokeswoman Lisa Malloy also said customers would be able to make free in-network calls to Sprint or Nextel subscribers starting sometime next month.

Underpinning the merger is a strategy of pursuing the fast-growing wireless business and of abandoning the local phone land-line business, which operates in 18 states, including Virginia. Local phone providers have seen their customers steadily desert them in favor of mobile phones and Internet phone service.

Sprint Nextel also is expected to ally with cable companies that want to add a mobile phone offering to their bundles of television, Internet and local phone service.

In the eight months since the two companies announced their merger, their total wireless subscriber base, including mobile phones sold under the Sprint and Nextel brands as well as those of partners, has risen nearly 10 percent.