Jailbreak

Jailbreaking is a process that sets up the /etc/fstab to mount all iPhone partitions for read and write, giving you full access to the system and removing the locks imposed by Apple.

With jailbreak, you will have access to packages available through Cydia, such as OpenSSH and themes for customization.

Here I jailbroke an iPhone 3G with iOS 4.2.1. On theiphonewiki.com, I found several programs capable of performing the jailbreak on Windows, I tested two:

Greenpois0n: Despite the iPhone 3G being listed as compatible in the README, it is not compatible.

Redsn0w: Formerly QuickPWN. Quite simple, it is what I used to jailbreak my iPhone.

Redsn0w

Download redsn0w_win_0.9.6rc19.zip or a newer version. Make sure the version performs an untethered jailbreak, so you don’t need to connect the iPhone to the computer after each reboot.

Download the 4.2.1 firmware and restore the iPhone using iTunes, using this firmware. Since this is the last version for the iPhone 3G, you can restore normally, and the firmware will be saved in C:\Users\Julio\AppData\Roaming\Apple Computer\iTunes\iPhone Software\Updates\iPhone1,2_4.2.1_8C148_Restore.ipsw.

Start redsn0w, connect the iPhone via USB, and turn it off. On the first screen, select the firmware you used in the previous step. On the second screen, check the options Install Cydia, Enable multitasking, and Enable battery percentage.

Follow the process to enter DFU mode, and the jailbreak will start.

Installing useful programs

After restarting the iPhone, look for the package called OpenSSH in Cydia and install it.

Access the iPhone via SSH from a computer. The username is root and the password is alpine:

julio@julio-acer ~  $  ssh root@10.0.0.3

root@10.0.0.3's password:
Julios-iPhone:~ root#

Change the root password:

Julios-iPhone:~ root# passwd
  Changing password for root.
  New password:
  Retype new password:

Also, change the password for the mobile user:

Julios-iPhone:~ root# passwd mobile
  Changing password for mobile.
  New password:
  Retype new password:

Installing a terminal

The default terminal is MobileTerminal. The version available in Cydia is incompatible, download the new version from the website and send the .deb package to the /var/root/Media/Cydia/AutoInstall folder:

julio@julio-acer ~  $  scp MobileTerminal_520-1_iphoneos-arm.deb root@10.0.0.3:/var/root/Media/Cydia/AutoInstall
  root@10.0.0.3's password:
  MobileTerminal_520-1_iphoneos-arm.deb          100%  232KB 232.4KB/s   00:00

Cydia will automatically install the terminal. Restart the iPhone for the icon to appear.