I have a question about the small box plug that came with the DROID RAZR MAXX.

It has two USB ports. First of all, I just opened my phone and started charging it for the first time.

What is the second USB port used for? Can it only charge a second phone? Or, can I use this to connect to my computer as a cradle? Would I then need a separate cable?

Previously on my old phone, I had two cables: one for charging and one connected to my computer. It would be nice if I could just plug this into one cable and it does both but I don't know how the box functions.