Sprint Nextel and Clearwire yesterday announced a letter of intent to jointly construct a nationwide mobile WiMAX network using the considerable 2.5 GHz spectrum held by the two service providers.

During a conference call yesterday, officials for Sprint Nextel and Clearwire outlined the agreement, which calls for the joint network to cover 100 million potential customers in the U.S. by the end of 2008 and be nationwide at an undetermined point in the future.

Sprint Nextel plans to lead the early buildout in the top 50 cities and is expected to provide coverage to 62% of the U.S. population, which represents about 185 million potential subscribers. Clearwire is expected to lead the buildout in the rest of the nation, covering about 115 million potential subscribers.

Both service providers had announced WiMAX buildout plans, but many industry analysts doubted the viability of two companies offering services using the same technology in the already competitive wireless market. In particular, many questioned the wisdom of committing billions of dollars to the capital expenditures necessary to build out WiMAX networks.

Through the partnership, both companies hope to realize a nationwide buildout sooner and reduce capital expenditures significantly.

“We will be owning and operating a smaller footprint than if we were to build out this entire network on our own,” Sprint Nextel Chairman and CEO Gary Forsee said.

Sprint Nextel plans to lead marketing efforts in the wholesale and enterprise sectors, Forsee said. Clearwire would get access to existing Sprint facilities—cell sites and backhaul—at commercial rates.

Definitive agreements for the partnership are expected to be finalized within the next 60 days. At that point, the agreement would be subject to review by the U.S. Department of Justice and the FCC—processes the companies hope to secure by the end of this year.