Sprint Nextel Corp expects to upgrade its high-speed wireless services network faster than it expected, sending its shares up more than 7 percent on Friday.

Shares in Clearwire, which Sprint owns most of, fell 15 percent after Sprint said at an investor event in New York on Friday that it hopes to use spectrum from Clearwire's rival LightSquared to bolster its network capacity.

Sprint, the No. 3 U.S. mobile service, said it will launch its high-speed service by the middle of 2012 and expects to complete its upgrade by the end of 2013.

Sprint talked about a five-year plan for upgrading its network when it first discussed the project in December.

The company, which started taking orders for the Apple Inc iPhone on Friday, said that while the device is more expensive than others, the iPhone will be quite accretive to its profits over time.

Chief Executive Dan Hesse expects the device to be one of Sprint's most profitable, but he did not give specifics.

Sprint plans to upgrade its network using Long Term Evolution, the same high-speed wireless technology used by its two bigger rivals AT&T Inc and Verizon Wireless, a venture of Verizon Communications Inc and Vodafone Group Plc.

LightSquared, which is backed by hedge fund manager Phil Falcone, needs regulatory approval to build a network using the spectrum Sprint hopes to use.

(Reporting by Sinead Carew and Supantha Mukherjee. Editing by Gerald E. McCormick and Robert MacMillan)