NEW YORK -- Sprint Nextel Corp. and Clearwire Corp. today said they had canceled their plan to combine the high-speed wireless networks they are building.

The breakup is a blow to Clearwire, which already has a network in some parts of the country, based on the WiMax wireless technology. Sprint's buildout, using the same technology, would have complemented Clearwire's coverage.

Shares of Clearwire fell $3.44, or 19 percent, to $14.59, setting a new 52-week low. Shares of Sprint lost 12 cents, or less than 1 percent, to $16.42.

Sprint and Clearwire agreed in July to team to work out a plan to combine their networks.

Today, they said they were not able to able to "resolve complexities" in the deal.

The recent departure of Sprint CEO Gary Forsee has brought the company's commitment to WiMax, which had been touted as a cost-effective competitor or replacement to cellular broadband networks.

Interim CEO Paul Saleh has reaffirmed Sprint's plans, which involve spending $5 billion through 2010, but a new, permanent CEO could scuttle those plans.

Clearwire was founded by cell-phone pioneer Craig McCaw.

First Published: November 9, 2007, 6:00 p.m.