... 2, iPhone 3G/3GS , iPhone 4 /4s Use of digital audio amplifier, 2.0 channel high-power high tone quality output Four ... functional electronic switch (audio on-off switch, audio input selection volume +, volume -) easy to use User ... on the base With a 3.5mm audio input interface, support for other external audio device (such as MP3, MP4, etc.) A ...