The leak came yesterday from what appears to be a Staples memo to employees detailing the pre-order process leading up to the S4's launch.
The document from the retailer also mentions a May 1 debut on T-Mobile and a May 30 release on Verizon - more than a full month after AT&T starts S4 sales.
The Galaxy S4 launch dates are listed as "tentative" in the screenshot of the image that Engadget obtained, so the dates of course could prove inaccurate, but a hint is better than nothing.
Galaxy S4 pre-orders begin tomorrow
The leaked memo also indicates that Samsung Galaxy S4 pre-orders will begin tomorrow in Staples stores.
That announcement also revealed the official Galaxy S4 price on AT&T: $199 for 16GB and $249 for 32GB with a two-year contract.
The Galaxy S4 will likely set the benchmark for smartphones during the next year, with its 5-inch 1080p display, quad-core processor (in the U.S. and U.K. at least), and unique features like air gestures that allow it to detect a finger hovering over the screen to varying effects.
Can't wait? Check out TechRadar's latest hands-on Galaxy S4 review and keep an eye out for all the Galaxy S4 release date news we come across.