Sprint shares, up as much as 12 percent earlier on Friday, were halted and fell 7 percent when they resumed trading.
The phone company, which started taking orders for the iPhone Friday, said the phone is more expensive than others but will be ``quite accretive'' to its profits over time.
Chief Executive Dan Hesse said he expects the device to be one of Sprint's most profitable, but he did not give specifics.
The No. 3 U.S. mobile service said it plans to upgrade its high-speed wireless services network faster than it previously expected, leading analysts to question how the company would pay for the upgrade along with its commitment to carry the iPhone.
``Seeing all these balls in the air is a little scary,'' said Evercore analyst Jonathan Schildkraut.
Shares of Clearwire, which Sprint owns most of, fell 30 percent after Sprint said at an investor event in New York Friday that it hopes to use spectrum from Clearwire rival LightSquared to bolster its network capacity.
Clearwire shares were down to $1.44.
LightSquared, which is backed by hedge fund manager Phil Falcone, needs regulatory approval to build a network using the spectrum Sprint hopes to use.
Sprint also said it must raise money in the markets and could borrow against its revolving credit line.
It 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 still expects its network upgrade to save about $11 billion, mostly through closing its older iDen network.
It also said operating income before depreciation and amortization should improve by 4 percent to 6 percent from current levels by 2014.
Bernstein Research analyst Craig Moffett worried that Sprint could have problems with its service while it sets aside spectrum for the network upgrade.
It is not clear how the company would avoid ``creating a capacity gap'' when there will be big demands on the network, he said, particularly from users of the iPhone.
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.
(Reporting by Sinead Carew and Supantha Mukherjee. Additional reporting by Liana B. Baker, Editing by Gerald E. McCormick, Robert MacMillan and John Wallace)