HTC had officially announced the One X+ smartphone a few days ago, and now the unlocked handset is available for pre-order in the United States as well.

The SIM-free device is already up for pre-order in the UK via online retailer Clove, and now online retailer Expansys USA has put the unlocked HTC One X+ up for pre-order in the U.S. Pricing and exact shipping, however, are still unknown.

"If you place a pre-order for this product now, we will not ship or charge your credit card without confirming you still wish to proceed when stock arrives. There are no cancellation charges," explains Expansys USA.

AT&T customers, however, should keep in mind that the handset up for pre-order is an unlocked European model, which means it will not work on the carrier's LTE network.

Meanwhile, the official AT&T version of the HTC One X successor, the One X+, should be available by the end of November. The unlocked European version from Expansys may work on AT&T's HSPA and 3G networks, however.

The HTC One X+ is largely similar to the regular One X smartphone. It packs the same Nvidia quad-core Tegra 3 processor, though clocked at 1.7GHz, and has 1GB of RAM. The handset also sports a 4.7-inch laminated Super LCD2 display with a resolution of 1280 x 720, protected by Gorilla Glass 2.

Other features include an 8-megapixel rear-facing camera, with a BSI sensor and f/2.0 lens, as well as HTC's ImageSense technology. The smartphone also has a 1.6-megapixel front-facing camera for video chats, and connectivity includes Wi-Fi, Bluetooth, and NFC. The One X+ is powered by a 2,100mAh battery.

This version of the HTC One X+ also packs 64GB of internal storage. The AT&T version offers less storage because the built-in LTE radio takes up more space. The One X + also comes with the latest Android 4.1 Jelly Bean operating system and HTC Sense 4+ user interface out of the box.

In conclusion, the unlocked device comes with more internal storage than the AT&T version, but no LTE. The AT&T version will be able to run on the carrier's faster 4G LTE network, but you will have to wait a little bit longer. Will you wait for the AT&T version or pre-order the unlocked model now?