CNET/Marguerite Reardon

Sprint has quietly flipped the switch on its 4G LTE network in some areas of San Francisco, New York, and Washington, D.C., suggesting an official launch may be close at hand.

While confirming a report that first appeared in The Verge, a company spokesperson did not specify which sections of the cities would have access to the speedier network.

"During a pre-launch phase, customers with 4G LTE-capable devices may begin to see 4G LTE coverage in these areas and are welcome to use the network even before it officially launches," Sprint representative Roni Singleton told CNET today, adding that the company plans to announce commercial availability of the 4G LTE network on the San Francisco peninsula in the coming months.

"Over time, the markets will fill in until coverage largely matches the existing nationwide 3G footprint," she said.

The carrier, which lags behind Verizon Wireless and AT&T with its LTE network, announced in October that it would expand into an additional 22 markets -- including San Francisco -- "in the coming months," although it did not give a specific time frame. CNET reported late last year that LTE may not arrive in the major markets of New York and San Francisco until March.

Sprint has been playing catch-up in terms of 4G LTE, lagging far behind rivals Verizon Wireless and AT&T. Under Sprint's Network Vision plan, which is estimated to cost $4 billion to $5 billion, the company is shutting down its iDEN-based Nextel network, moving to 4G LTE, and simultaneously improving its 3G CDMA coverage.

So far, it has largely rolled out LTE in smaller markets. Sprint noted the faster wireless service is currently available in 49 networks, and it has announced nearly 200 more areas where LTE is on its way.