If you jailbreak your 3.0 beta2 iPhone, you can install OpenSSH, but it will work only for SCP (or SFTP: FTP over SSH). This means that you can put/get files, but you can't use the terminal.
Seems like the problem with the terminal is because of missing libraries: in fact, the BSD subsystem is not installed by that unofficial jailbreak.
So, here it is my solution.
Download this file: Download package from Sendspace
Extract it. It is the whole bundle that is installed when you pwn your 2.x phone. What we need in it is the BSD Subsystem: in particular, some libraries not installed by the new jailbreak.
(for those wondering where it came from... It's just a package extracted from PwnageTool)
Just copy all the files inside the usr/lib folder into your phone (using SFTP, for example Cyberduck or Filezilla) in /usr/lib
That package contains everything; however, you might need just libraries (install other binaries only if you need them - and if you know what you are doing!).
That should be enough to use OpenSSH!
PS: this method has been tested by a couple of users and they both reported it worked. however, I can't guarantee it's perfect, and I ASSUME NO RESPONSIBILITY at all. as always, use at your own risk. EDIT
Some users reported crash when copying all libraries. Maybe this is not 100% safe...
My suggestion is to copy JUST needed libraries, and never overwrite existing files.
Make sure you know what you are doing before copying any file!!!