Concerns regarding a liquidity crisis at Clearwire Corp. (CLWR) have been swirling around since the company expressed its decision to skip paying interest rates in order to conserve cash last month. Such concerns can be put to rest today; however, following the announcement that Sprint Nextel Corp. (S) has consented to paying $1.6 billion to Clearwire Corp. over the next four years. Sprint also agreed to a network pact and toyed with the possibility of a future equity infusion.

Shares of Clearwire tacked on more than 18 percent following the announcement as it became evident that fears of bankruptcy were unfounded. That brings Clearwater, which confirmed it would have funding enough to fulfill a $237 million debt interest payment due today, up close to 40 percent for the 5 day trading period.

Sprint is a leading shareholder in Clearwire as well as the company’s largest customer. The investment serves both corporations by supplying Sprint with continued access to high speed broadband access and providing Clearwater with the funding boost it needs to effectively complete the new fourth-generation network it has been developing. Clearwire’s intentions to construct its own LTE network for its most populated consumer bases is part of its effort to compete with AT&T (T) and Verizon (VZ), both of which are further along in the process, having already developed their services. Their advancements threaten to continue to grab marketshare away from Clearwire, making the completion of the network a priority both for Clearwire, and Sprint considering the influence that would have over the price of the stock.

Erik Prusche, Clearwire’s CEO noted the agreement “cements” the relationship with Sprint. In the months preceding the deal, after Clearwire said it would need $1 billion in order to fund its network, some investors were alarmed that the relationship with Sprint was nearing an end as the carrier sought to build out its own high-speed network. After having agreed to pay $926 million for the unlimited use of Clearwire’s network through 2013 though much of that worry has dissipated.

Prusche assured shareholders in an interview that the company had achieved its three top priorities in securing funding, extending its relationship with Sprint and paying the interest on its debt, but the company’s failure to diversify its funding are setting off alarm bells. Analysts cited in the Wall Street Journal said there remains cause  for concern, as Sprint failed to diversify its funding. The company reportedly needs more financing than Sprint will provide and while vendor financing was being considered, the company did not divulge any details.

Some are hoping that Sprint’s support of Clearwire will prompt some outside investor interest and bolster an increased sense of security with the investment. The idea that the company was verging on bankruptcy was a natural deterrent for many investors aware that the company’s fate is so closely tied to Sprint’s decisions.