AT&T will be opening up pre-orders for Samsung’s latest flagship device – the Galaxy S4 – tomorrow. There still isn’t a launch date for the device just yet, but rumors from last week suggested that we’d be seeing it sooner rather than later. A new leak says just as much.

Engadget received an internal memo from an anonymous source that lists the S4 release date across three major carriers – AT&T, Verizon and T-Mobile. As expected, the Galaxy S4 will be hitting AT&T first on April 26. T-Mobile subscribers won’t have to wait much longer as the device will launch for them on May 1. Those with Verizon will unfortunately have to wait a month as its launch is scheduled for May 30.

The memo says the above launch dates are tentative at the moment so things can change. The whole thing could be fake as well, but it certainly fits with previous comments from T-Mobile’s CEO when he said that the S4 would be coming to the network on May 1.

If these tentative launch dates stay the same, we should start seeing the Galaxy S4 going up for pre-order on T-Mobile and Verizon shortly. The leaked memo doesn’t mention any other carriers though so those waiting for word on Sprint’s pre-order and launch plans will probably have to wait a little longer.

On a final note, those interested in the S4 should probably get their pre-order in as soon as they open for your respective carrier. The memo says that inventory will be “highly constrained” at launch. We can hope that a repeat of last year’s Galaxy S III launch won’t be repeated, but Samsung may very well run out of stuck as soon as it launches.