Amazon.com Inc. is preparing to release a smartphone in the second half of this year, according to people briefed on the company's plans, part of a broad push into hardware that would pit it against Apple Inc. and Samsung Electronics Co.

The retailer has been demonstrating versions of the handset to developers in San Francisco and its hometown Seattle in recent weeks, these people said. People briefed on the company's plans have been told that Amazon aims to announce the phone by the end of June and begin shipping phones...