The Sony Ericsson Xperia X10 that was first released in the UK back in March has finally made its way to the U.S. The company’s flagship Android smartphone will be available on the AT&T network from August 15 and, despite the delay, will still be running the Donut edition of Android, version 1.6 – apparently because Sony Ericsson has been having trouble modding its add ons to suit Android 2.1.

It’s worth revisiting the phone’s features that had us so impressed just a few short months ago. The X10’s 4-inch touch display may have been upstaged by the Retina Display of the iPhone 4, which was released while U.S. customers twiddled their thumbs waiting for the X10’s release, but the X10’s 4-inch touchscreen is still a pleasure to behold.

Back when we reviewed the X10 the custom UI was a bit sluggish despite the use of a 1GHz Snapdragon processor. Thankfully, Sony Ericsson has since released a software update that focused on improving the phone’s speed and responsiveness, as well as improving the speed of messaging tasks and the camera UI. The phone comes with aGPS along with an 8.1 megapixel camera that boasts smile detection, face recognition, autofocus and LED flash. It also comes with a 2GB microSD memory card on top of the phone’s 1GB onboard memory, but will accept microSD cards up to 32GB.

Staking the phone’s claim as an entertainment and communications device are two signature applications: Mediascape and Timescape. Mediascape gathers music, photos, videos and content from the phone’s memory card and online, letting users browse, search and listen and share media from one unified view, while Timescape is a communication application that automatically organizes social interactions from sources such as Facebook, Twitter, emails and text messages in chronological order.

If you’re considering purchasing the phone, be sure to check out our review, which pits the X10 against the HTC Desire.

The Sony Ericsson Xperia X10 will be available from August 15 through AT&T for US$149 on a two-year plan.