Apple ipod

How I can download OS 4.0 beta on my iphone?

I do not know where to go? I'm lost? Or is it something you buy with a new iPhone I have a 16GB 3G.

The beta is available for registered users (mainly developers). But the developers as I have seats available for those who are interested in trying the beta. Also part of your question about the new iPhone. Also with the new iPhone, you just get to try before.

How To Jailbreak iPhone 3G Firmware 4.0 Beta 1 with redsn0w 0.9.5