Shares of NII Holdings Inc. (NASDAQ:NIHD) resumed their descent Monday when the international wireless carrier acknowledged what investors suspected the prior week: A $1.4 billion investment from Grupo Televisa SA (NYSE:TV) in NII's Nextel Mexico unit had unwound.

The wavering deal between NII and Telvisa has been one of the most closely watched developments in the wireless business over the last week. The other is Clearwire Corp.'s (NASDAQ:CLWR) exploration of funding options to continue building its wireless broadband network in the U.S.

NII and Clearwire have ambitious plans to build infrastructure to carry the deluge of wireless data and content. Both also have ties to pioneering wireless entrepreneur Craig McCaw. However, the carriers face much different circumstances. NII, of Reston, Va., won Mexican spectrum licenses in an auction this summer, and is developing a third-generation, or 3G, wireless network. Televisa may have had a change of heart about its direction. The Mexico City television and media group said earlier this month it would pay $1.2 billion for a stake in Spanish language media company Univision Communications Inc.

NII said it will build the Mexican wireless network by itself. The company has a $2.4 billion pile of cash, but it also has an ambitious agenda that includes plans to bid for spectrum in Brazil.

"There are a lot of growth plans over the next several years," says Allyn Arden of McGraw-Hill Cos.' (NYSE:MHP) Standard & Poor's, noting that NII also has convertible notes due in 2012. "The amount of cash is probably not great enough to cover their funding plans over the next few years," Arden says. "They probably have reasonable access to the credit markets, whether U.S. credit markets or local bank or vender financing."

Chris King of Stifel Nicolaus & Co. observes that NII is one of the world's fastest-growing telecoms and is levered at just .4 times projected 2011 Ebitda. In conversations with some large NII equity holders, he says, the sentiment is that "there are a lot cheaper ways for the company to raise capital than to sell 30% in its highest margin business." The analyst suggested that the company could easily refinance the 2012 notes.

Clearwire, meanwhile, announced Monday that it will launch its 4G wireless broadband service in New York on Nov. 1, and Los Angeles on Dec. 1. The move will bring the company into the nation's largest markets. While operational momentum may be building, Clearwire faces more of a financial challenge.

S&P warns that Clearwire's cash may hit "dangerously low levels" in the first quarter of 2011. It needs more capital to continue its buildout, and is said to be auctioning spectrum.

Clearwire has excess spectrum, and clearly has pressing needs. However, spectrum is a vital asset in wireless.

Walt Piecyk of BTIG LLC says that demand for data is only rising. Technology can increase the network capacity, but spectrum is a necessity. Piecyk suggests its value will only grow. "If you can hold onto the asset, better to hold onto it and borrow against it than sell it," he says.

Financing has been a year-end ritual for the Kirkland, Wash., company. In November 2009, Clearwire announced a $1.5 billion equity infusion. Clearwire closed a merger with Sprint Nextel's WiMax arm that included a $3.2 billion investment from backers in December 2008.

The market is eagerly awaiting a new source of funding.

Clearwire CEO Bill Morrow is speaking Wednesday at the 4GWorld conference. His talk is entitled "Mobile Data Tidal Wave: How Clearwire's 4G Network is Meeting Today's Pent Up Demand for Mobile Broadband."

Clearwire could assauge more immediate concerns with a plan to address the pent up demand for capital.