In a big win for Google Inc., Dell Inc. plans to introduce a smart phone using Google software on the AT&T Inc. cellular network, according to people briefed on the plans.

Dell is expected to launch the phone in the U.S. as soon as early as next year, these people said. With an AT&T deal, all four major U.S. cellular networks would carry phones using Google's Android operating system, a key step in the Internet giant's attempt to extend its dominance of the personal-computer world to mobile phones.

The...