What is the other space on my iPhone, and how do I clean it up?

I just bought a new iPhone 4.It has only 8GB of memory, and a whole 2.4GB of that is taken up by mysterious "other" information. I can't figure out what this stuff actually is or how to get rid of it. I've thought about it being contacts, text messages, etc… But I just barely got the phone. Clearing out the few messages I had didn't make any difference anyway. What can I do to get that cleaned up?

The other is the space the software takes up, you can't do nothing about that. I have the 64GB iPhone 4S and I have 57.4 available. That means 6.6GB is taken up by the other.