iPhone vibrating for no reason

[M A V I C]

Borrowed a power cable. It doesn't vibrate when charging like the dock was. This is the alarm clock: http://www.amazon.com/gp/product/B003M8H...tl?ie=UTF8&tag=amazoncom080-20&linkCode=as2&camp=1789&creative=390957&creativeASIN=B003M8HWDA

I now see it says "iPhone 3G/3GS" - guess that means it doesn't support the iPhone 4? Can't believe they'd sell a product that couldn't support any iphones from the past few years.