Sprint announced its second 4G-capable smartphone, the Samsung Epic 4G, which  will be available beginning Tuesday, Aug. 31, online and in stores for $249.99 with a two-year contract.

The Android-based Epic 4G is part of Samsung’s Galaxy S line of AMOLED smartphones. The Epic features a slide-out qwerty keyboard, differentiating it from Sprint’s other 4G handset, the HTC Evo 4G, which features only a virtual qwerty.

The Epic 4G boasts such high-end specs as 720p video capture, HDMI out, 1 GHz Hummingbird processor, 5-megapixel camera with LED flash, Wi-Fi, Bluetooth and mobile hot spot functionality. The Epic will come running Android 2.1 (Éclair), but Sprint says it plans to upgrade the phone to Android 2.2 (Froyo) in the coming months.

The Samsung smartphone is Sprint’s second phone to support the carrier’s WiMAX service.  Sprint now offers WiMAX in 48 markets. In 2010, the company says it expects to launch it in multiple markets, including Boston, Cincinnati, Cleveland, Denver, Los Angeles, Miami, Minneapolis, New York, Pittsburgh, San Francisco and Washington, D.C.

For those who want to be sure they can get their hands on an Epic, Sprint also announced today that for the first time, the carrier will allow customers to place pre-orders for the Epic. Customers can reserve their Epic beginning tomorrow while supplies last.

Variations on the Samsung Galaxy S are also available on T-Mobile (Vibrant) and AT&T (Captivate), with Verizon Wireless launching it version (Fascinate) in the coming months.