Samsung Electronics Co.'s flagship Galaxy S4 won't go on sale as planned Wednesday morning on T-Mobile USA Inc.'s website because of a shipment delay, dealing a setback to a smartphone that garnered lukewarm reviews Wednesday.

T-Mobile, which has been angling to be the first carrier to offer the device in the U.S., pushed the debut back until April 29. The Galaxy S4 is getting a staggered release in the country, with AT&T Inc., Sprint Nextel Corp. and Verizon Wireless planning their own introductions in coming weeks.

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T-Mobile blamed the postponement on "an unexpected delay with inventory deliveries" in a message on its website. Jessica Redman, a U.S. spokeswoman for Suwon, South Korea-based Samsung, said her company didn't have an immediate comment on the T- Mobile release.

The delay signals that the new device may get off to a slower start in the U.S., where Samsung aims to supplant Apple Inc. as the top-selling smartphone maker. The phone is getting a tepid reception from reviewers, including AllThingsDigital's Walt Mossberg, who said its software is "especially weak."

Rich Jaroslovsky, a reviewer for Bloomberg News, called the Galaxy S4 "soulless." "Several of its advanced features don't work very well, and it feels more like a collection of functions than a smoothly integrated experience," he wrote in his review.

Other reviewers were more favorable, including Mashable's Christina Warren, who called the product the best smartphone based on Google Inc.'s Android software.