Samsung is finally releasing its Galaxy S2 smartphone in the United States and would compete with iPhone 4, which is considered as one of the best phones in the U.S. market. The smartphone also rivals the rumored specs of the forthcoming iPhone 5, which analysts expect to come in September or October.

Galaxy S2, which is touted as iPhone killer, is fastest-selling Samsung phone ever with 5 million devices sold in 85 days in Europe and Asia.

Galaxy S2 is coming to AT&T, T-Mobile and Sprint, whose version is called as Samsung Epic 4G Touch.

On Sprint, Epic 4G Touch will cost $199.99 (excluding taxes) with a two-year contract.  AT&T version, which is the thinnest of the three, is also expected to be on the same lines in the range of $250 to $300, while T-Mobile hasn't announced pricing or availability details.

Galaxy S2, which runs on Android 2.3 Gingerbread OS and sports Samsung's TouchWiz UI, comes with an 8-megapixel camera with flash and can record HD video in 1080p offering the richest video content on a smartphone. The phone also has the front-facing 2-megapixel camera for video chat.

The Galaxy S2 has a Voice Talk feature allowing users to give their Galaxy S2 device voice commands, including voice dial, text message, navigation, music, Web browsing and search. When docked into the car dock, the Galaxy S2 automatically defaults into Voice Talk mode. Users can instantly activate the Voice Talk application by a long press on the search key.

Galaxy S2 features six-axis motion sensing using an accelerometer and gyroscope that support advanced touch screen gestures, including motion to zoom in on images, silence a ringing phone, and even move widgets on the menu screens.

Galaxy S2 also supports popular video conferencing services like Skype, Fring, Qik and Tango and has a Super AMOLED Plus touchscreen display.

Epic 4G Touch is a powerful smartphone that delivers vibrant and exciting content at lightning fast speeds. This device is ultra-thin yet ultra-powerful with a screen that rivals anything else in the industry, Fared Adib, vice president-product development at Sprint.

Galaxy S2 is expected to come to Sprint's network on Sept.16 and would be launched on AT&T from Sept.18.

There are only minor differences among the three U.S. versions of Galaxy S2. AT&T's version would have a 4.3-inch screen, while the Sprint and T-Mobile versions sport a 4.5-inch display.

On the connectivity front, the smartphone will use HSPA+ network on AT&T and T-Mobile and WiMAX on Sprint.

Meanwhile, the AT&T version is the thinnest at 8.89 millimeters, usurping the Sprint version with its 9.65 millimeters.

Rest of the specifications is same for the three versions. Following are the specifications of Galaxy S2:

Operating system: Samsung Galaxy S2 features the Android OS version 2.3 (Gingerbread).

Processor: Samsung Galaxy S2 comes with dual-core 1.2GHz ARM Cortex-A9 Mali-400MP GPU Exynos processor with 1GB RAM.

Screen: Galaxy S2, in general, sports a 4.3-inch Super AMOLED screen with 800x480 screen resolution.

Size: Generally, Samsung Galaxy S2 has a dimension of 125.3 x 66.1 x 8.5 mm and weighs 116 g.

Camera: Samsung's Galaxy S2 has an 8-megapixel camera with auto-focus, LED flash, geo-tagging, touch focus, face and smile detection and image stabilization. Galaxy S2 captures HD video at 1080p at 30 fps.

Storage: Galaxy S2 boasts 16GB internal storage and can be expandable up to 32GB via a microSD card.

Input features: Galaxy S2 has features like Gorilla Glass display, TouchWiz UI v4.0 and Gyroscope sensor.  

WLAN/Bluetooth: Galaxy S2 has Wi-Fi 802.11 b/g/n DLNA support and an added Wi-Fi Direct feature. Samsung's phone uses advanced 3.0+HS version Bluetooth with A2DP and EDR.

Battery: Galaxy S2 features a Li-Ion 1650 mAh battery