Sprint and Clearwire reached a billion-dollar-plus deal today that will allow the WiMAX operator to make a key debt payment on time and keep its network up and running for the next four years.

Clearwire President and CEO Erik Prusch had warned that the company was considering defaulting on the $237 million payment, due today, because of a cash shortage that threatened the company's ability to operate. Clearwire said today it made the interest payment.

Prusch called the deal an "important step" toward securing the future of Clearwire.

"Today's announcement further cements the mutually beneficial relationship between our two companies," Prusch said. "It is an important step toward meeting Clearwire's key goals of extending our current 4G network arrangement, securing a commitment to our future LTE Advanced-ready network and funding the business."

Sprint is providing Clearwire with a much-needed influx of cash – $926 million for unlimited access to its WiMAX network during 2012 and 2013. The companies' previous arrangement priced access on a per-megabyte basis. Beginning in 2014, Sprint will go back to usage-based pricing for Clearwire's WiMAX services.

Sprint recently announced it would transition to LTE but plans to keep selling WiMAX devices that run on Clearwire's network through at least 2012. Under the terms of the new agreement, those devices, which come with two-year contracts, will be supported through the life of the contract. Sprint will have access to Clearwire's WiMAX network through at least 2015.

Sprint will also provide $350 million in cash for Clearwire's TD-LTE rollout, which can't begin until the company raises $600 million in new funding. However, the LTE funding comes with some fine print: Clearwire must meet certain build-out targets by June 2013 to get the prepayments, which are set to be spread out over the next two years. Clearwire will seek additional funding separate from Sprint's financing before it begins construction of the LTE overlay network.

Sprint said last month that it plans to use Clearwire's LTE network for supplemental capacity to its own service. The two operators announced today that they are collaborating on a build plan for the LTE network and will jointly pick cell sites that cover Sprint's high-usage areas. If the deployment of the network goes according to schedule, Sprint will launch the first devices using Clearwire's LTE network in 2013.

Beyond the money for Clearwire's LTE network, Sprint also agreed to provide additional equity funding to the company, a point of contention between the two operators. If Clearwire is able to raise between $400 million and $700 million in new funding, Sprint will contribute up to $347 million of its own money on a pro rata basis consistent with its 49.6 percent stake in Clearwire.

Investors welcomed the news, sending Clearwire's stock up 23 percent in morning trading.