AT&T today rolled out its fastest HSPA+ smartphone yet, the Samsung Infuse 4G. The Infuse is AT&T’s only HSPA+ phone certified at HSDPA CAT 14 (downlink, 14 Mbps) and HSUPA CAT 6 (uplink, just under 6 Mbps).

The Infuse will be available in AT&T company-owned stores and online on May 15 and will cost $199.99 with a two-year contract and no mail-in rebate.

AT&T and Samsung are billing the Infuse as the “world’s thinnest” smartphone, coming in at 8.99mm thick. Otherwise, the Infuse falls on the larger side of the smartphone spectrum, featuring a 4.5-inch Super AMOLED Plus touchscreen. The Infuse comes running Android 2.2 (Froyo) and features a 1.2 GHz processor, 8-megapixel rear-facing camera, 1.3-megapixel front-facing camera, Wi-Fi, Bluetooth and a 2GB MicroSD card (expandable up to 32GB).

AT&T is throwing in a few extras with the Infuse. The first 500,000 Infuse 4G units sold will include a $25 voucher for consumers to get started on downloading content from Samsung’s Media Hub. Additionally, the Infuse 4G comes with a 2GB microSD card with preloaded trailers for upcoming summer movies.

The device will also come with a pre-loaded version of Angry Birds that features an exclusive hidden level for Infuse 4G customers.

Jeff Bradley, the company’s senior vice president of mobile devices, used the Infuse announcement as occasion to let loose details confirming the impending debut of the HD7S, the last of AT&T’s first-generation Windows Phone 7 handsets, according to a report from Engadget.

Bradley also reportedly hinted that AT&T will begin allowing its Android customers to download apps from third-party repositories, starting with Amazon’s Appstore.