If there were sighs of relief at AT&T, there were whoops of joy at the Kansas City headquarters of U.S. Sprint. Last week the two companies landed the biggest telephone contract in history: to replace the cranky, 25-year-old federal long-distance telephone system with a modern, fiber-optic system that would be capable of transmitting not only conversations and data but also video images. The deal, which is worth upwards of $25 billion, was a boon for AT&T. The company recently projected an annual loss for this year of up to $1.7 billion -- its first in more than 100 years. For struggling Sprint, the contract was a godsend.