Sprint is turning on LTE in some parts of San Francisco, Washington D.C. and New York City. 

While these markets haven't officially launched, a Sprint spokeswoman Kathleen Dunleavy confirmed "more and more reports of Sprint customers discovering LTE on their 4G LTE devices in San Francisco, Washington D.C. and New York City."

According to Dunleavy, Sprint is turning on LTE in preparartion for official launches in the markets. 

"This is done in order to test and prepare the network. It is one of the many ways our network team ensures that 4G LTE meets Sprint’s standards," she said, adding that many of the sites will remain turned on and customers can continue to access the service on their devices. 

"The service will get better and reach more and more neighborhoods as we continue our buildout – this is a taste of what’s to come," she said. 

While Sprint's LTE deployment is still siginificantly behind rivals AT&T's and Verizon Wireless', the carrier will be aggressively pursuing a 4G buildout in 2013. 

As part of its Network Vision initiative, Sprint said during a 4Q earnings call that on air sites have nearly doubled in last 90 days, with LTE live in 58 cities total and nearly 170 more expected in the coming months. Sprint said construction has started in more than 450 cities, with more than 19,500 sites now ready for construction.