Apple has released the iPhone 4 Dock specifically for the new smartphone. The dock can charge the smartphone or sync data when connected to a computer via USB. The dock also connects the smartphone to a TV or projector through audio-video composite or Apple's component cables. There is also an audio-line out port to hear music on speakers.
The iPhone 4 Dock is "compatible only with iPhone 4," Apple specifically states on its Web site. The smartphone's predecessors had a separate design that prevents them from fitting in the dock.
The dock is priced at US$29 and is on Apple's Web site.