It's a really simple knockoff from Apple's nearly identical $40-50 product, but this one is smaller and lighter - lighter not being an entirely great thing, seeing how it's a docking base.
The line-out outputs the audio, but doesn't let you control the volume (probably set on 75% vol). Charges and holds the phone perfectly. It also docks and charges my iPhone 4 with no problems, even though it doesn't fit perfectly.
The iPhone 3G dock is an essential part of using your iPhone 3G. It's so much more convenient having not to unplug and carry the dock around with you; when you can have one ready and waiting for you at work and at home. The iPhone 3G dock has been designed and tested specifically for the Apple iPhone 3G. This USB 2.0 sync data cable can connect your iPhone or iPod directly or through a dock to your computer's USB port for efficient syncing and charging or to the Apple USB power adapter (not included) for convenient charging from a wall outlet.